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[CONTRIBUTION FROM THE LABORATORIESF THE DIVISIONF

INSECTICIDE

INVESTI-

GATIONS,

B UR EAU

F

ENTOMOLOGYND PLANTUARANTINE . S. DEPART-

MENT OF AGRICULTURE,WASHINGTON,

. C.

]

CONSTITUENTS

O F

PYRETHRUM FLOWERS. IV.* THE SEMI-

CARBAZONES

O F

PYRETHRINS

I

AND

I1

AND

O F PYRETHROLONE?

H. L. HALLER AND F. B.

LAFORGE

Received Februarg 16, 1956

The conclusions that have been reached by numerous investigators re-

garding the relative insecticidal value of the two toxic principles of pyr-

ethrum flowers, pyrethrin I and pyrethrin

11

show wide variance. This

lack of agreement seems to be due to the fact that the pure pyrethrins

have never been available for biological tests. Our nvestigations in this

field have for their object the study of methods by which these pure

pyrethrins might be obtained.

A considerable advance toward this accomplishment was made in the

improvement in the method of preparing concentrates high in total pyr-

ethrins and the separation of these concentrates into fractions in each of

which one of the separate pyrethrins predominates, described in

a

previous article,2 to which the reader is referred for complete details.

The preliminary operations whereby the crude starting material, a com-

merical product consisting of the petroleum-ether extractives of pyrethrum

flowers,

is

freed from fats, waxes, and fatty acids, and which gives

a

con-

centrate containing

70

per cent. total pyrethrins, need not be reviewed here.

The process by which this concentrate is separated into fractions in

which the separate pyrethrins are concentrated is based on the observation

that they have different solubilities in diluted acetic acid and in petroleum

ether. When the

70

per cent. concentrate is dissolved in petroleum ether

and the solution is agitated with acetic acid containing the proper amount

of water, the pyrethrin I and the pyrethrin I1 are found to be very un-

equally distributed in the separated liquids, most of the pyrethrin

I

being

* For art icle

I11

of this series see ACREE,

SCHAFFER,ND HALLER,o u r . Econ

Ent., in press.

t We are indebted to F. A. Acree, Jr., and

P.

S. Schaffer for technical assistance

throug hout th is invest igat ion and to J.

R.

Spies for th e microcombustions.

GNADINGER,

. B., P yret hru m Flowers. Minneapolis, 1933 p. 92.

LAFORQE,

.

B.,

AND HALLER, . L.,

J. Amer.

Chem. SOC. 7 1893 (1935).

38

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CONSTITUENTS

OF PYRETHRUM FLOWERS

39

in the petroleum-ether solution and most of the pyrethrin I1 in the acetic

acid. Since the impurities present in the concentrate tend to follow the

pyrethrin

I,

the method

is

more favorable for the purification and concen-

tration of the other toxic principle, pyrethrin 11. By repetition of the

process just described with the material isolated from the acetic acid solu-

tion, a further concentration of pyrethrin I1 is attained.

As a result of these operations three concentrates are obtained, one

that has a content of about 4 0 4 5 per cent. pyrethrin I together with 12-14

per cent. pyrethrin

11

another containing 80-83 per cent. pyrethrin I1

with

3-5

per cent. pyrethrin

I,

and an intermediate fraction tha t contains

both pyrethrins in about equal proportions.*

After many applications of this method we have not found it necessary

to make any important changes. Having noticed, however, that in the

first separation the impurities tended to go with the fraction in which

pyrethrin

I

predominated, we found it advantageous to keep the inter-

mediate fractions separate for retreatment, because these fractions had

a

higher total pyrethrin content and, when separated in a new series of

operations, yielded concentrates higher in the respective pyrethrins. For

instance, the pyrethrin I1 concentrate obtained from the intermediate

fractions contained about

87

per cent. of pyrethrin

11,

and the correspond-

ing pyrethrin I concentrate about

57

per cent. of pyrethrin I.

As already reported2 concentrates of 80 per cent. pyrethrin I1 content

can be distilled in the molecular still and yield material which analyses

indicate to be substantially 100 per cent. pyrethrin 11. For reasons that

will be given later, it seems doubtful that the product

so

obtained repre-

sents the natural, unaltered compound. The best available concentrates

of pyrethrin I were regarded as too impure to offer promise of satisfactory

results by this method of direct distillation.

After we had accomplished an approximate separation

of

the two pyr-

ethrins, it seemed promising to make

a

study of their isolation by other

means. The investigations of Staudinger and Ruzicka3 are based on the

isolation of the pyrethrins as semicarbazones, which are practically their

onl;y known crystalline derivatives. The best starting material available

to them for the preparation of the semicarbazones was a concentrate con-

taining

50-60

per cent. of total pyrethrins present in about equal amounts,

from which concentrate a mixture of the semicarbazones of both pyrethrins

was obtained. The semicarbazone of pyrethrin

I

proved to be the less

soluble, and by repeated recrystallization it was possible, with great loss

*

Pyre th r in

I

was de termined by th e method of Seil, Soap, 10,

no. 5, 89 (1934);

pyre th r in I1 by the method of Haller and Acree, Ind Eng. Chem.

Anal

Ed., 7 343

(1935).

STAUDINGER

.,

AND

RUZICKA,

.,

Helv. Chim. Acta

7

177

(1924).

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40

H. L. HALLER AND

F.

B. LAFORGE

of material, to obtain preparations of it which approached the state of

purity. When the semicarbazone was hydrolyzed, the free ester, pyr-

ethrin I, was obtained. This product when distilled under reduced pres-

sure, on analysis, agreed fairly well with the formula C21H3003, but it

yielded only 50 per cent. of a semicarbazone apparently identical with the

one from which it was obtained. The semicarbazone of pyrethrin

I1

was

not obtained in a state even approximating purity.

Staudinger and Ruzicka, in their principal investigations on the struc-

ture of the pyrethrins, employed the semicarbazone mixture that had been

freed from extraneous material by crystallization. Since the cyclic ketonic

alcoholic component, pyrethrolone, was shown to be common to both

pyrethrins, its semicarbazone could be obtained by saponification of the

mixture of semicarbazones of both the pyrethrins, and the acid components

could be isolated and separated subsequently. The pyrethrins themselves

were then resynthesized from pyrethrolone and the respective acid com-

ponents, chrysanthemum acid and chrysanthemum dicarboxylic acid

methyl ester. Although these resynthesized pyrethrins possessed high

insecticidal properties, they did not yield satisfactory semicarbazones,

and i t is doubtful that they represent the natural unaltered toxic principles.

As a more careful study of the semicarbazones seemed indicated, the

present investigation of their isolation and properties was undertaken

with the employment of the concentrates now available in which the pyr-

ethrins had been to a large extent segregated. We first turned our atten-

tion to the preparation of the semicarbazone of pyrethrin I1 from the

80-87 per cent. concentrates.

PYRETHRIN

I1

SEMICARBAZONE

Instead

of

using sodium acetate, as did Staudinger and Ruzicka, we

employed pyridine after we found that better yields of the semicarbazone

were obtained with this base. Contrary to what was expected from

reports in the literature, the semicarbazone of pyrethrin

I1

was readily

obtained in quantitative yield and practically pure from the pyrethrin 11

concentrate. The same compound is also obtained when sodium acetate

is employed. The semicarbazone was easily recrystallized and melted

sharply at

165 .

Its composition as shown by analysis agreed with the

formula C23H33N305r C23H31N30~. n saponification in methyl-alcoholic

solution under the conditions prescribed by Staudinger and Ruzicka, it

yielded the semicarbazone of pyrethrolone that melted a t 208 with decom-

position and had the other physical properties described by these authors.

The free ester, pyrethrin 11, was obtained from its semicarbazone by

hydrolysis with aqueous oxalic acid solution, the method used by Stau-

dinger and Ruzicka to obtain pyrethrin

I

from its semicarbazone.

This

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CONSTITUENTS

OF

PYRETHRUM

FLOWERS

41

method is unsatisfactory, because it involves partial saponification and

decomposition, and the yield of crude ester is only 30 per cent. of the

theory. Various experiments were made by these authors and also by us,

but

without discovering

a

more satisfactory method of hydrolysis. I t

appclars, however, that whatever of the pyrethrin I1that survives the treat-

ment, is essentially unaltered, because when the crude product is again con-

verted into the semicarbazone the original compound is regenerated in good

yield.

The pyrethrin I1 that we obtained by molecular distillation of the

pyrethrin I1 concentrate, as mentioned above, had the composition re-

quired for pyrethrin

11

C23H3006

or

C23H2806,s shown by analysis, and

a preliminary test against flies made by

F. L.

Campbell, of the Division

of

Control Investigations of this Bureau, showed it to possess a high order

of

toxicity. When treated with semicarbazide under the same conditions

as those used to prepare pyrethrin semicarbazones, a product was obtained

that crystallized only partly on complete removal of the solvent and

that was evidently different from the semicarbazone of pyrethrin

I1

de-

scribed above. It must be concluded that some intramolecular change

took place on distillation.

When the semicarbazone preparation was saponified, it yielded only an

insignificant amount of pyrethrolone semicarbazone, indicating that some

change had taken place in that part of the molecule.

PYRETHRIN I SEMICARBAZONE

The semicarbazone of pyrethrin I was obtained from the pyrethrin

I

concentrate by the method employed for the preparation of pyrethrin I1

semicarbazone. This concentrate is of lower total pyrethrin content than

that of pyrethrin I1 and contains, besides a large amount of noncrystalline

products, a considerable quantity

of

the crystalline (nontoxic) pyrethrol.

The latter crystallizes on standing and may be removed to a large extent

by filtration. After

24

hours the semicarbazone formation was finished

and the separation of the crystalline product was completed by cooling in

a freezing mixture. The crude product was thus obtained in about quan-

titative yield, based on the total pyrethrin content of the concentrate. An

additional quantity was obtained from the mother liquor as described in

the Experimental Part. This material is much less pure and may contain

substances other than pyrethrin semicarbazones. The main portion,

after washing and drying, melted at 90-100 . The material is difficult

to purify. Although it can be readily crystallized from a number

of

solvents such as acetone, alcohol, and toluene, it is only by repeated re-

crystallization that a fairly pure product is obtained. After two recrystal-

lizations from acetone

and

one from alcohol or toluene, it melts not very

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42

H. L. HALLER AND

F. B.

LAFORGE

sharply at about 112-1 14'. By further recrystallization the melting

point can be raised to

118'.

We have never obtained

a

sample entirely

free of methoxyl, the quantity found indicating the presence of roughly

10

per cent. pyrethrin I1 semicarbazone, this in spite of the fact that the

latter is very soluble in the solvents employed. The analytical results

made on various samples agree only approximately with the formula,

CnH33N303

In an attempt to obtain the semicarbazone of pyrethrin I in pure con-

dition, the material was hydrolyzed with aqueous oxalic acid solution as

described in the case of the pyrethrin I1 semicarbazone. The yield of

the free ester in this case was also about 30 per cent. The material was

then reconverted into the semicarbazone, which was obtained in good

yield, and the properties of the regenerated semicarbazone were the same as

those of original material, the melting point being about

115-117 .

When

the crude pyrethrin I obtained from the semicarbazone in a similar experi-

ment was distilled under a reduced pressure of about

1

mm. and the semi-

carbazone was prepared from the distillate, a yield of only 50 per cent.

was obtained. After recrystallization it melted at about the same tem-

perature as the original semicarbazone. The low yield indicates that

pyrethrin I is also to

a

large degree altered by distillation. However,

the fact that the semicarbazone isolated has the same properties as the

original semicarbazone indicates that at least part of the pyrethrin I sur-

vives the distillation unaltered. The analytical results obtained for these

regenerated semicarbazones showed significant divergences from the re-

quirements of the formula C22H33N303 When the semicarbazone of

pyrethrin

I

is dissolved in carbon tetrachloride, it separates in the form

of long needles and exhibits physical properties different from those of

the original material. The substance has not yet been thoroughly in-

vestigated.

SEMICARBAZONE OF PYRETHROLONE

The semicarbazones of pyrethrin I1 and pyrethrin

I

give the semicar-

bazone of pyrethrolone in quantitative yield on saponification in methyl-

alcoholic solution with 1 mol of sodium ethylate under the conditions

prescribed by Staudinger and Ruzicka. This reaction seems to proceed

somewhat more slowly in the case of pyrethrin I. Pyrethrin I1 semicar-

bazone yields the semicarbazone of pyrethrolone and

a

mixture of about

equal parts of chrysanthemum dicarboxylic acid and chrysanthemum

dicarboxylic acid monomethyl ester in the form of their water-soluble

sodium salts and also a considerable quantity of chrysanthemum dicar-

boxylic acid dimethyl ester. That the saponification of the mixed semi-

carbazone proceeds in this manner has already been pointed out by

Staudinger and Ruzicka.

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C O N S T I T U E N T S

O F

P Y R E T H R U M F L O W E R S

43

Pyrethrin

I

semicarbazone yields, besides pyrethrolone semicarbaxone,

the monobasic chrysanthemum acid, which is volatile with steam. When

large quantities are saponified,

a

small amount of

a

nonvolatile acid is

obtained which has not yet been identified.

For the isolation and identification of small quantities of chrysanthemum

acid and chrysanthemum dicarboxylic acid, it has been found convenient

to take advantage of the fact that both form crystalline paraphenyl-

phenacyl esters.

A

corresponding crystalline derivative of chrysanthe-

mum dicarboxylic acid methyl ester has not been obtained.

Pyrethrolone semicarbazone crystallizes well from acetone, ethyl ace-

tate, or methyl alcohol. It is difficultly soluble in all these solvents, in

which it forms supersaturated solutions. The compound is easily purified,

and melts at a little above

200

with gas evolution. We have found the

deconiposition point

t o

be about 208 .

Pyrethrolone semicarbazone has been assigned the formula C12H19N302

by Staudinger and Ruzicka on the basis of three reported analyses. The

figures reported by them agree fairly well with this formula, although

those for hydrogen are low by more than the limit of error. In our first

few analyses of this compound we observed a still lower hydrogen content

and

a

higher carbon content than are required by the above formula. In

fact, our own analyses agree within experimental error with a formula

with two less hydrogen atoms,

i.e.

C12H17N302.Having noted the dis-

crepancy, we made

a

large number of combustions, by both the micro

and semimicro methods, on several samples of this compound, all of

which confirmed the formula with 17 hydrogen atoms. The theoretical

differences between the two formulas in question are 0.39 per cent. for

carbon and 0.78 per cent. for hydrogen.

HYDROGE NAT ION OF PYRE T HROL ONE SE MICARBAZ ONE

The structural formula of pyrethrolone semicarbazone, according to

Staudinger and Ruzicka,

is

CHCH2CH=C=CHCHs

C=N-NHCONHz

OHC-

/ \

H2C

On hydrogenation four atoms of hydrogen are added to the double

bonds, giving tetrahydropyrethrolone semicarbazone. We also prepared

this compound by saponification

of

tetrahydropyrethrin

I1

semicarbazone.

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44 H

L. HALLER

AND

F.

B. LAFORGE

In both hydrogenation experiments the observed volume of hydrogen

absorbed corresponded to the addition of four atoms to pyrethrolone and

pyrethrin I1 semicarbaxones, respectively. The analyses of the hydro-

genated pyrethrolone semicarbaxone obtained by both processes indi-

cate that it should be represented by the formula C12H21N302nstead of

Cl2HZ3N3O2. he theoretical differences between these formulas are 0.50

per cent. for carbon and

0.76

per cent. for hydrogen. The analyses re-

ported by Staudinger and Ruxicka for this compound agree (except for

one hydrogen determination) with the formula Cl2HZ1N302s found by us.

We have not yet prepared pyrethrolone itself, but it is apparent that the

analyses reported by Staudinger and Ruzicka for this compound agree

best with the formula ClIHls02, although even in this case the hydrogen

content reported is lower than would be expected.

The discrepancies between the accepted formulas for pyrethrolone semi-

carbazone and tetrahydropyrethrolone semicarbazone and the observed

analytical results seem to be of great importance in their bearing on the

structures of these compounds and hence of the pyrethrins themselves.

If

pyrethrolone contains two hydrogen atoms less than is now supposed,

a

revision of its formula, possibly by the assumption of the presence of a

second ring structure, will be necessary. Such an assumption would

disturb the harmony of the conclusions that have been reached with re-

spect to the part of the pyrethrin molecules that is concerned with pyr-

ethrolone.

EXPERIMENTAL

Pyrethrin 11

semicarbazone

has been prepared by us several t imes with s l ight

variations in th e procedure.

Twenty-four grams

of

pyre th r in

I1

concentrate containing 81 per cent.

of

pyr-

e t h r i n I1 was dissolved in 8 cc. of 95 per cen t. a lcohol and 35 cc. of pyridine. A

solution of

10

grams of semicarbaxide hydrochloride in 12 cc. of water was added.

After s tanding 3 d a y s

at

room temperature, the solution was diluted with about

3 volumes of water an d extr acte d with ether. Th e ethe r solution was washed several

t imes wi th water , then wi th d i lu te hydrochlor ic ac id , and aga in wi th water . It

was then dr ied and evapora ted on the s team bath . Crys ta ll izat ion began when mos t

of th e ether had been removed, and was completed by cooling in th e ice box. Th e

crystall ine material was removed by fi l trat ion and washed by suspending in ether

and again fil tering. Th e ether washings together with th e firs t mother l iquors viere

evapora ted to a syrup, which readi ly c rys ta l l ized , and the separa ted mater ia l was

fi l tered from the syrupy m other l iquors with suction on s i lk. Th e crystal s were

washed with ether and dried. Bo th crops melted

at 163-164 .

Th e to ta l y ie ld was

16.5 grams, or 75 per cent. of th e theory . T he pure compo und is very difficultly

soluble in ether, b ut i t can be recrystallized by dissolving in a large volume

of

t h e

solvent and evapora ting to a smaller volume. It can be crystall ized from 95 per

cent. alcohol, in which it is much m ore soluble.

It

is sti l l more soluble in the other

common solvents.

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CONSTITUENTS OF PYRETHRUM FLOWERS 45

In anothe r experiment th e proport ions employed were 45 grams of concentrate

containing 79.5 per cent. of pyrethrin 11 15 cc. of 95 per cent. alcohol, 65 cc. of

pyridine, 18 grams of semicarbazide hydrochloride, and 20 cc. of wa ter. T h e yield

of mater ia l wi th the same mel t ing point as th a t f rom th e previous exper iment was

33.5 grams,

or

81 per cent. of th e theor etical 41.3 grams.

I n a th i rd exper iment 49 grams of py reth rin I1concentrate was dissolved in 175 cc.

of 95 per cent. alcohol, 75 cc. of pyridine, and 20 grams of semicarbazide hydro-

chloride in 25 cc. of w ate r was adde d. After 2 da ys most of the solvents were re-

moved by dis t i l lat ion un der reduced pressure, a nd the sep arat ed cry stal mass was

suspended in water an d fil tered off on suction. Th e material was washed with water

and then suspended i n e ther ; the c rys ta ls were f i lte red off and aga in washed wi th

th e s ame so lven t. Th e

ethe r mother l iquor a nd washings were washed with water, dilute hydrochloric acid,

and aga in wi th water , dr ied , and concentra ted t o a syrup. Th e syrup was al lowed

to crystall ize, after which th e solid material was removed by fi l trat ion with suction

on si lk. An addit ional qu an ti ty of material was th us obtained, which afte r washing

wi th e the r amoun ted to 8 . 9 grams. Th e tot al yield was therefore 38.4 grams, or

97 per cent. of t he theo ry.

Cry stals are seldom obtained directly from th e pyridine-alcohol solution. Th is

sometimes occurs, however, when the concentrate employed is of the order of 85-

87 per cent . pyre thr in 11. One recrystallization gives an analytically p ure product

me l ting a t 164-165 .

T he yield of pra ctically pu re material was 29.5 grams.

Anal

Calc 'd for C23H33N306: C , 64 .03 ; H , 7.66; Tu , 9.74.

Found: C, 64.19, 64.19, 64.46, 64.40, 64.19;

H,

7.51, 7.64, 7.37, 7.40, 7.45;

Pyre th r in I1 semicarbazone is also obtained from the same concentrates with

the em ployment of sodium acetate instead of pyridine, th e preparation having been

repea ted under th e condi t ions employed by Staudinger and Ruzicka to show th a t

pyridine has no influence on the product obtained. Th e yield, however, is smaller

when sodium ace tate is used. Two parallel experiments were made with a concen-

t ra te conta in ing 84.1 per cent. of pyrethrin 11, pyridine being employed in one and

sodium ace ta te in the o ther .

Th ree and th ree- tent hs grams of t he concentrate was dissolved in 10 cc. of alcohol

and < cc. of py ridine, an d to this solution 1.2 gram s of sem icarbazide hydrochloride

in 1.5 cc. of water was adde d. After sta nd ing 2 days th e solu t ion was d i lu ted w i th

water an d the separa ted materia l was ext rac ted wi th e ther . Th e solu t ion was

washed with water and dilute acid, dried, and th e solvent evaporated. Th e crystal-

l ine ma teria l was recrystall ized from ether. Th e yield was

1.6

grams, and the

melting point 165'.

Th ree grams of th e same concentrate was dissolved i n 10 cc. of alcohol, an d solu-

ti on s of 2 grams of sodium acet ate in 1.5 cc. of water and 1.2 gram s of sem icarbazide

hydrochloride in 1.5 cc. of wa ter were add ed. Afte r 2 days th e reac t ion product was

isolated as described above and 0.8 gram of recrystallized m ater ial was obtain ed.

I t melted likewise

at

165 .

hrydrolysis of pyrethr in ZZ semicarbazone.--?'wo an d nin e-te nth s gram s of pyr-

e th r in I1 semicarbazone was shaken a t 100 for 7 hours wi th

a

solu tion of

6

grams of

oxalic acid in 40 cc. of water. T he reaction product, a dark-red oil, was extr acte d

from

the aqueous solution with petroleum ether. A large am oun t of t a r remained

undissolved. Th e petroleum-ether solution was washed firs t with potassium car-

bonate solution an d then with water, dried, and evaporated. T he result ing red oil

C23HaiN305: C, 64.34; H, 7.27; N , 9.79.

N, 9.85, 9.69.

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46

H . L. HALLER

A N D F. B .

LAFORGE

gave a q ua l i ta t ive tes t for n i trogen. It was reconverted into th e semicarbazone by

dissolving in 3.5 cc. of alcohol and 1.5 cc. of pyridine and adding 0 . 4 gram of semi-

carbazide hydrochloride in 0 . 5 cc. of w at er . Afte r 2 days th e reac t ion mixture was

worked up in the manner a l ready descr ibed, and gave

0.5

gram of recrystallized

semicarbazone, m.p. 163 . When mixed with pyrethrin I1 semicarbazone (m.p.

165 ), the melting point was 163 .

Semicarbazone from the pyrethrin I I obtained by molecular distillation.-One an d

eigh t-ten ths gram s of a pyre th r in I1preparation t ha t had been twice dis t il led in the

Hickman s t i l l ,* and which f rom analys is by th e methoxyl metho d conta ined 97.7

per cent. of pyrethrin 11, was dissolved in 20 cc. of alcohol, and 2.7 cc. of pyridine

and

a

solu tion of 0.7 gram of sem icarbazide hydrochloride in 1cc. of wat er was adde d.

After 3 days water was added and th e reac tion product was ext rac ted wi th e ther .

The ether solution, after being washed with acid and water, gave on evaporation

1.2 grams of a colorless syrup. After several day s this syr up only par t ly crystal-

l ized, b ut i t was n ot possible to isolate th e crystall ine material .

It

was dissolved

in

10

cc. of m eth yl alcohol to which

6

cc. of a

1

per cent. solution of sodium me thy late

1

mol) was added. After abo ut 10 day s th e small qu an ti ty of separated crystals

was filtered off and recrystall ized from acetone. Th e qu an ti ty of pure substance was

abou t 0.1 gram. It melted a t 205 with decomposit ion, in agreement wit h th e

melting point of p yrethrolone semicarbazone. Since thi s compound is obtained in

qua nti ta t ive yield from the semicarbazone of p yre thrin I1 under t he condit ions de-

scribed, i t is app aren t th at some change has taken place in t he process of dis t i l lation

of

pyre th r in 11.

Hydrogenation of pyrethrin I I semicarbazone.-Two gra m s of py re th ri n I1 semi-

carbazone, m.p. 165 , was hydrogenated wi th p la t inum oxide ca ta lys t in e thyl

ace tate solution. After 15 minu te s 205 cc. of hydrogen, corresponding to four atom s,

had been absorbed and the reaction had s topped. Th e solvent was removed under

reduced pressure and th e residue dissolved in ether. Th e ma teria l obtained aft er

evapora tion of t he e ther c rys tal l ized on t rea tm ent wi th d i lu te e thyl alcohol . Th e

crude product was washed wi th a l i t t le cold d i lu te potass ium carb onate solu tion

and, afte r drying, was recrystall ized by dissolving in 20 pa rt s of wa rm e thy l alcohol,

filtering, and slowly adding

8

t o 10 pa rts of w arm water.

It

m e lt ed a t 139-140O .

An al. Ca lc' d fo r C23H37N305: C, 63.45; H , 8.50.

Found : C, 63.43, 63.36; H , 8.14, 8.11.

Th e same compound was obta ined f rom the hydrogenated p yre thr in

I1

concen-

tr at e on tre atm en t wit h semicarbazide in alcohol-pyridine solution. Two and four-

ten ths grams of a pyre th r in I1 concentra te wi th abou t 82 per cent . pyre thr in I1 was

hydrogenated wi th p la t inum oxide ca ta lys t in e thy l ace t a te so lu tion . After

45

minutes 322 cc. of hy drogen had been absorbed and the reduced m ater ial was sepa-

ra ted f rom the solvent . Th e mater ia l was d issolved in 8.5 cc. of a lcoho l an d 3.6 cc.

of pyrid ine to which 1 gram of semicarbazide hydrochloride in 1.5 cc. of water was

added. After s tanding 2 day s th e semicarbazone was isolated by m eans of ethe r

and recrystall ized from dilute alcohol. It mel ted a t 141-142'.

When mixed with

the product o bta ined by d i rec t hydrogenat ion of pyre th r in I1 semicarbazone, the

mixture melted at 141-142 . Th e two substances ar e therefore identical .

C23H3~N305:C, 63.74; H, 8.08.

Anal.

Calc'd for

C23H~7N306:

C, 63.45; H, 8.50.

Found : C, 63.72, 63.56, 63.50, 63.33, 63.59; H, 8.10 8.14, 8.09, 8.12 8.09.

C23H36N806: C, 63.74; H , 8.08.

*

See LaForge an d H allera.

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CONSTITUENTS

O F

PYRETHRUM FLOWERS 47

Saponification of hydrogenated pyrethrin ZZ semicarbazone.-One an d two- tenths

grams of hydrogenated py reth rin

I1

semicarbazon e was dissolved in 30 cc. of methyl

alcohoI, and 1 cc. of methyl-alcoholic sodium me thy late containing 0.01 gram of

sodium was added. After being ke pt for

12

days in the ice box, the solvent was

removed under reduced pressure and t he residue washed wi th e ther and t hen wi th

wa te r . It was recrystall ized from ethyl acetate and melted with decomposit ion

a t 196 .

A n d . Calc 'd for C12H23x302: C, 59.75; H , 9.54.

Found : C , 60.20, 60.05; H , 8.90, 8.76.

C12H21N302: C, 60.25; H, 8.78.

Pyrethrin

Z

semicarbazone.-Fifty-five grams of pyrethrin I concentrate from

which pyrethrol had been removed by cooling and filtering on silk, and which con-

tained 45 per cent. of py reth rin

I

and abou t 14 per cent. of pyrethrin

11,

was dis-

solved in 190 cc. of alcohol and 8 cc. of py rid ine . A so lu tio n of 22 grams of semi-

carbazide hydrochloride in 27 cc. of w ater was add ed, an d th e solution was allowed

to s t and a t room tem pera tu re for

24

hours.

It

was placed in the ice box overnigh t

and th e crystallization completed by cooling in a freezing mixture. Th e crystall ine

ma teria l was removed by fi l trat ion and washed w ith cold alcohol, then with di lute

acid, and finally with water. T he dried ma teria l weighed 32 grams. T he alcoholic

mother liquor and alcoholic washings were concentrated under reduced pressure,

afte r which water w as added, causing the separation of a n oily product which pa rt ly

crystallized on cooling. It was ag itated with petroleum eth er, which dissolved the

liquid products , leaving a crystall ine material which was removed and washed w ith

petro leum e the r . It weighed

12

grams.

T he first crop of c ry sta ls was recrystallized

twice f rom ace tone and once f rom a lcohol and m el ted a t abo ut 112 . Th e mater ia l

obta ined f rom the mother l iquors has a lower melting point and is very soluble in

most reagents . It probably is

a

mixture of pyrethrin

I

semicarbazone wi th th e

semicarbazone of py reth rin I1 and oth er unknown products .

Concentrates of pyrethrin I obta ined f rom th e in te r med ia te f rac tions resul t ing

from the init ial separations contain no pyrethrol and are of a higher pyre thr in

I

con tent . Th e material employed for th e two preparations described below contained

57

per cent. of pyrethrin I and 14.8 per cent. of pyrethrin

I1

as shown by analysis.

Thir ty- two grams of th is m ater ia l was t rea ted w i th semicarbaz ide in th e same

mann er a s described above, the propo rtions of th e reagents being: alcohol 112 cc.,

pyridine

40

cc., semicarbazide hydrochloride 12.8 grams, and water 16 cc. After

s t and ing a t room tempera tu re fo r 24 hour s, crys tallization was completed by cooling

in a Freezing mixture and the cry stals were washed wit h alcohol, acid, and water.

The yield was 24 grams, and 5.7 grams of th e impure mat erial was obtained from

the m other l iquor in the mann er a l ready described. This impure subs tance was

dissolved in a small volume of alcohol, out of which 1.3 grams crystall ized. It

melted at a b o u t 105 . Th e alcoholic solution was evaporated under reduced pres-

sure, leaving a product t ha t was easi ly soluble in e ther bu t could not be made to

crystall ize from thi s solvent. On addit ion of petroleum ethe r a crystall ine pre-

c ip i ta te was obtained which m el ted a t abou t 70, and

a

methoxyl determination

ind ica ted th a t it contained 36.7 per cent. of pyr ethr in

I1

semicarbazone. Eighteen

grams of pyre thrin

I

concentrate containing 57 per cent. of pyrethrin I ob ta ined

f rom intermediate fractions was converted into the semicarbazone in the manner

jus t described, th e proportions of reagents em ployed being alcohol 60 cc., pyridine

27 cc., semicarbaz ide hydrochloride 7.2 grams, and water

9

cc. Th e yield of crystal-

l ine material ob taine d by direct crystall ization, washing, a nd drying was 13.5 grams,

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48

H .

L .

HALLER

AND

F.

B .

LAFORGE

a n d

2.5

grams was ob t a ined f rom the mother l i quors by t r ea tm ent wi th wa te r an d

petroleum ether.

In a l l these preparat ions th e tota l yie lds of semicarbazones were higher tha n th at

calcula ted f ro m the tota l pyrethr in content of the concent ra tes

as

found by analysis.

Th is indicates th at substances othe r tha n th e pyre thr in semicarbazones are present

in th e crude crys ta ll ine products .

For purif icat ion only the material obtained by direct crystal l izat ion was em-

ployed, and recrystal l izat ion was accompanied by considerable losses in the f i rst

operat ions. Usually two recrystal l izat ions from acetone and one from alcohol

or

toluene gave products mel t ing a t

112-114'.

By fur ther recrys ta l l iza t ion i t was

poss ible to ra ise th e mel t ing point t o

117-118 .

Man y an alyses of t he recrystal l ized

products have been made.

Ana l. Calc'd for C&&303:

C, 68.22; H, 8.53.

Found for materia l w i th m.p.

114-115':

C,

68.33, 68.50;

H ,

8.33, 8.37;

for mater ia l wi th m.p.

113-114':

C,

68.59, 67.98, 68.58; H , 8.42, 8.17, 8.52.

Quantitative saponification of pyrethrin Z semicarbazone.-Since pyrethrin I semi-

carbazone is t he este r of

a

monocarboxylic acid, i t should be possible t o determ ine

the quant i ty of pyrethr in

I1

semica rbazone t ha t migh t be p resen t by qua n t i t a t i ve

saponif icat ion. Many at tem pts were made t o accompl ish this determinat ion.

When samples of the purest material available were saponified by boiling for

a

few minu tes with

0.1N

alkal i and b ack- t i t ra t in g wi th s tan dar d acid, values c lose to

theoret ical were obtained. When i t was found th at pyreth r in I1 semicarbazone

required

30

minutes boil ing with

0.25N

alkal i for complete saponificat ion and the

pyre th r in I semicarbazone samples were t reated with

0.25.V

a lka l i under t h e same

condit ions, th e values obtained ind icated th e presence of a bo ut

15

per cent. of pyr-

e th r in

I1

semicarbazone. Since th e resul ts were no t sharp , th e figures obtained wil l

be omit ted.

It

is possible th at th e semicarbazone of som e compound othe r t ,han

pyrethrin 11 diff icul t to remove by crystal l izat ion, is present in the pyrethrin I

semicarbazone preparat ions.

Th e great difference in solubil ity between th e semicarbaaones of p yre thrin I a n d

pyre thr in I1 indicates th at the la t ter should be eas i ly e l iminated.

Hydrolys i s of

pyrethrin semicarbazone.-Three gram s of py ret hr in I semicarba-

zone (m.p.

114 ),

which had been twice recrystal l ized from acetone and once from

alcohol , was agi tated with

a

solution of

6

grams of oxalic acid in 40 cc. of water at

100

o r

7

hours . Th e red oil was extracted f rom the aqueous solut ion wi th pet roleum

ether , the pet roleum ether solut ion was washed wi th sodium carbonate , and the

solut ion dr ied a nd evaporated.

The material obtained weighed

1.4

grams. It was

dissolved in 5 cc. of alc oho l an d 2 cc. of pyridine, and

0.6

gram of semicarbazide

hydrochloride in 0.8 cc. of wa ter was added . After 48 hou rs th e solut ion was cooled

an d th e crystals were removed and washed with cold alcohol . Th e yield was

0.9

gra m , After recrystal l izat ion from acetone,

0.7

gram of crystal l ine material

was

obtained.

It

softened

at 114'

and mel t ed a t

117-118'.

Anal.

Six grams of th e purified semicarbazone of pyre thr in

I

was agi ta ted for

7

hour s

with a Bolution of

9

grams of oxalic acid in

60

cc. of wa ter a t

100 .

The react ion

produ ct , which was isolated and sep arated from acid const i tuents, weighed

3.1

grams.

It was dist il led a t 2 mm. pressure . The qu ant i ty of mater i a l t h a t d i s ti ll ed at

175-

180

was

1.1

grams. It

was

converted into semicarbazone, the proport ions of re-

agents being the same as

in

other preparat ions. Th e yield of crude crystal l ine

Calc'd for C22Ha3N303: C,

68.22;

H ,

8.53.

F o u n d : C,

68.82, 68.66; H, 8.47, 8.45.

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CONSTITUENTS OF PYRETHRUM FLOWERS 49

product was 0.55 gram, mel t ing a t 105-110 . It was recrysta l lized and mel ted

at

111-~112 .

T h e

small yield indicates th at p ar t of th e material was changed on dis ti l lat ion, yielding

products that do not form crystall ine semicarbazones.

No crystall ine products could be obtained from th e mother l iquor.

Ana l .

I yrethrolone semicarbazone by saponiji cation

of

pyrethr in 11 semicarbazone.-

Twenty-five grams of pure pyrethrin I1 semicarbazone was dissolved in 100 cc. of

methyl alcohol, and 120 cc. of 0 . 5 N sodium methyla te (1 mol) and 6 cc. of water

were added to th e cooled solution. After s ta nd ing for 5 day s in the ice box, t he solu-

t ion was decanted f rom the heavy crys ta l l ine c rus t th a t had formed. Th e crys ta ll ine

material was washed with methyl alcohol and, when dry, weighed 9 grams . The

alcoholic solution was concentrated t o a small volume under reduced pressure, a nd

water was added, causing the separation of

a

finely divided solid ma terial. T he

suspension was ext rac ted wi th pe t ro leum e the r and separated f rom t he solvents by

fil trat ion. After drying i t was combined with the material deposited from th e

reaction mixture, and all was recrystall ized from methyl alcohol. Th e recrystal-

lization was accomplished by boiling the finely ground material with about 1 l i te r

of me thyl a lcohol und er reflux, filter ing from a fraction of a gram of insoluble ma-

te r ia l , and concentra t ing th e solu tion t o ab out 200 cc. Th e yield of pure m ate ria l

me lt ing a t 208 with decomposit ion was 12.5 grams, or ab out th e theoretical yield.

Under the given condit ions, the substance separates from methyl alcohol in flat

prisms which sometimes are half

a

centimeter long. It can also be recrystall ized

from acetone or et hyl ac etate , and in both these solvents th e compound is difficultly

soluble and sep arat es on concen tration of the solutions.

Calc'd for C22H~3Na03: , 68.22; H , 8.53; N, 10.85.

Found: C, 68.50, 68.53; H , 8.47, 8.45; N , 10.61.

A.naZ. Calc'd for C ~ ~ H ~ B N S O ~ :, 60.77; H, 8.02.

Found : C , 61.39, 61.08, 61.21; H , 7.62, 7.52, 7.53.

C12HiTN302: C, 61.26; H, 7.24.

Th e aqueous solution obtained on dilution of t he concentrated m other l iquor

was acidified with hydrochloric acid, and t he separated acid products were dissolved

in ether. Th e ethe r solution was dried and evaporated, yielding

9

gra ms of a mix-

tu re of chrysanthem um dicarboxylic acid and i ts monom ethyl ester. These were

sepw ated b y d issolving the syru py mater ia l in a smal l volume of chloroform and

addling petroleum ether. Chrysanthem um dicarboxylic acid crystall ized out on

standing. After recrystall ization and drying under reduced pressure at 60 , it

melted a t 168 . The petroleum ether-chloroform solution was evaporated, and the

residue, consisting of about 40 per cent. of chry santhe mu m dicarboxylic acid an d

GO per cent . of chrysanthemum dicarboxylic acid methyl ester as calculated from

the methoxyl content , was d issolved in e ther and shaken ou t wi th th e qu ant i ty

of

1N alkali calculated t o half-neutralize th e dicarboxylic acid. Th e aqueous solution

gave a product tha t conta ined 1.27 per cent. of meth oxyl corresponding t o 11.5 per

cen t. of ch rysan them um dicarboxylic acid meth yl ester an d, by difference, 88.5 per

cent. of chrysanthemu m dicarboxylic acid. Th e ether solution yielded a product

tha t conta ined 11.55 per ce nt. of m ethoxyl, corresponding to 79 per cent. of chry san-

them um dicarboxylic acid monomethyl ester.

The petroleum-ether solution obtained on extraction

of

the neutra l aqueous sus-

pension yielded on evaporation an oil that dis t i l led under 1mm. pressure

at

100-

102 .

The yie ld was 3 grams. It was the dimethyl ester of chrysanthemum di-

carboxylic acid.

A n a l .

Calc 'd for

CtrHlsO,:

2CHa0, 27.3.

Found : CHaO,

26.6.

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50

R L. HALLER

AND

F.

B

LAFORGE

Fifteen grams

of

pure pyre th r in I1 semicarbazon e was dissolved in 60 cc. of methy l

alcohol, th e solution was cooled, and t o i t 36 cc.

of

0.5 N (1 cc.

=

0.011 gram Na)

sodium meth yla te

(0.5

mol) was added. After s tan ding

3

day s in th e ice box, th e

separated p yrethrolone semicarbazone was fi l tered

off,

The alcoholic solution was

concentra ted to

a

small volume under reduced pressure and diluted with water.

Th e solu t ion toge ther w i th th e suspended crys tal l ine m ater ia l was extrac ted wi th

petro leum e ther , and the c rys ta l l ine mater ia l was f i l te red f rom the solvents and

added to th e subs tance tha t had s epa ra ted f rom the reac tion mix tu re . The to ta l

yield of d ry ma teria l was 8 . 4 grams. It was recrystallized from methyl alcohol.

The petroleum-ether washings were dried and evaporated, yielding 6.1 grams of

chrysanthemu m dicarboxylic acid dim ethyl ester. One gram of t he m ixture of

chrysanthemu m dicarboxylic acid and i ts m onomethyl es ter was obtained on acidifi-

cation and extraction of th e aqueous solution.

Parapheny lphenacyl ester

of

chrysanthemum acid.-An alcoholic so lu tio n of chr ys-

anthemum acid was neutralized with 0.25N alcoholic potash and th e calculated qu an-

ti ty of paraph enylp henac yl bromide' was added . T he solutio n was refluxed

for

1 hour, cooled, and the n diluted with an equal volume of wate r. Th e sep arat ed

crystall ine ester was removed by fi l trat ion, washed with water, a nd dried. T he

yield was qua nti ta t ive . T he ester was recrystallized from methyl alcohol and melted

a t 65'.

Anal.

Di-paraphenylphenacyl ester of chrysanthemum dicarboxylic acid.-The pro ced ure

for th e preparation of th is ester was the same as th a t described for the preparation

of th e ester of th e monocarboxylic acid. Th e ester was recrystall ized from toluene

or

acetone and me l ted a t 154 .

Calc'd fo r Cn'H2603: C, 79.56; H, 7.18.

Found: C, 79.21, 78.87; H , 7.16, 7.09.

Anal.

Pyrethrolone semicarbazone

by

saponification of pyrethm'n semicarbazone.-Three

grams of py reth rin I semicarbazone, m.p. 117 , was dissolved in 80 cc. of methy l

alcohol, the solution was cooled, and 6 cc. of methyl-alcoholic sodium methylate

containing 0.06 gram of sodium 1 mol) was added. After being kep t in th e ice

box for abo ut 2 weeks, th e crystall ine ma teria l was removed by fi l trat ion, a nd, when

dried, weighed

1.1

grams.

It

was recrystallized by dissolving in a large volume of

ace tone and concentra ting th e solu t ion to a bou t 60 cc. Th e dr ied crys ta ls mel ted

with decomposi tion a t 210 .

A

mixture wi th an equal pa r t of t he product obta ined

from the semicarbazone of p yret hrin 11, showed no depression in th e melting point .

Calc'd for C38H3406: C, 77.82; H, 5.80.

Found: C, 77.16, 77.98; H , 5.88, 5.82.

A nal. C alc'd for C I ~ H I ~ N ~ O Z :, 61.26;

H,

7.24.

Found :

C,

61.14, 60.77, 61.21, 60.89, 61.48;

H,

7.26, 7.16, 7.3 8, 7.35, 7.41.

Th e alcoholic m other l iquor yielded, on dilution with w ater, a n addit ional sm all

qu an ti ty of cry stall ine ma teria l and, on acidification and extraction w ith petroleum

ether, chrysanthemum acid.

Hydrogenation

o j

pyrethrolone semicarbazone.-one gra m of py reth rolo ne sem i-

carbaaone was dissolved in abo ut

100

cc. of a mixture of ethyl acetate and methyl

alcohol and reduced with 0 .2 gram of platinu m oxide cata lyst . After

30

minu te s

2

cc. of hydrogen ha d been absorbed, corresponding to th e saturat ion

of

two double

bonds. Th e solu t ion was f il te red and concentrated on the s team bat h and readi ly

D R A K E , . L.,

AND

B R O N I T S K Y ,.,

J

Am. Chem. SOC.,2, 3715 (1930).

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CONSTITUENTS O F PYRETHRUM FLOWERS 51

yieldlad the crystalline reaction product. It melted with decomposit ion at 196 .

It was identical with the compound obtained on saponification of hydrogenated

pyret#hrin 1 semicarbazone,

as

was shown by the mixed melting point 196 . Te tra-

hydropyrethrolon e semicarbazone is reported to melt a t 190 . Th e yield was quan-

t i ta t ive .

Anal .

Calc 'd

for

C12H23NaOz: C, 59.75; H, 9.54.

Fo un d: C, 60.50, 60.65; H, 9.14, 8.69.

Ci2H21N302:

C, 60.25;

H,

8.78.

SUMMARY

The semicarbazone of pyrethrin I1 has been prepared from the pyrethrin

I1

concentrate obtained by fractionation with immiscible solvents. It is

easily obtained pure and melts at 165 . On hydrogenation it yields

tetrahydropyrethrin I1 semicarbazone, which has the formula C23H36N306.

Pyrethrin I1 obtained by molecular distillation does not yield this semi-

carbazone, indicating that distillation produces some intramolecular

change.

Hydrolysis of the semicarbazone with oxalic acid solution yields un-

changed pyrethrin 11 which can be reconverted into the original semi-

carbazone.

The semicarbazone of pyrethrin I has not been obtained in analytically

pure condition. By repeated crystallization a nearly pure preparation

melting at 118 is obtained. The semicarbazone of pyrethrin I yields on

hydrolysis with oxalic acid substantially unchanged pyrethrin

I,

which

can be reconverted into the original semicarbazone.

Pyrethrin

I

is in part altered by distillation.

The semicarbazones of both pyrethrins yield the same pyrethrolone

semicarbazone on saponification. Pyrethrolone semicarbazone appears

from a large number of analyses to have the formula C12H17N302 instead

On hydrogenation of pyrethrolone semicarbazone, four atoms of hydro-

gen are absorbed and the resulting tetrahydropyrethrolone semicarbaxone

would be represented by the formula C12H21N302. The same compound is

obtained by saponification of tetrahydropyrethrin

I1

semicarbazone.

Chrysanthemum monocarboxylic acid and chrysanthemum dicarboxylic

acid form crystalline paraphenylphenacyl esters, which serve for their

isolation and identification.

of C12HigN302.