440 NICHOLLS: MANNICH’S METHOD FOR THE DETERMINATION OF MORPHINE

Mannich’s Method for the Determination of Morphine

BY JOHN RALPH NICHOLLS, B.Sc., F.I.C.

MANNICH, Handke and Baumgartenl describe a process for the quantitative determination of morphine by precipitation as the 2 : 4-dinitrophenyl ether. The precipitation is carried out in aqueous methyl alcohol solution, sodium or potassium hydroxide being used to bring about the reaction between morphine and 1 : chloro-2 : 4-dinitrobenzene.

In an examination of the method it was found that the proportion of alkali used was critical and that an excess over a certain amount caused the solutions to darken considerably in colour (owing to the decomposition of the chlorodinitro- benzene), and decreased the sensitivity when applied as a test for small quantities of morphine. For example, when equal quantities of a dilute morphine solution were treated as described by Mannich, but with varying concentrations of alkali, precipitates formed in solutions having alkalinities up to 0.02 N (calculated on the whole solution) within 2 hours, but solutions of higher alkalinities showed no precipitate within that time. In working with extracts of opium it was difficult

Publ

ishe

d on

01

Janu

ary

1937

. Dow

nloa

ded

by U

nive

rsity

of

Prin

ce E

dwar

d Is

land

on

31/1

0/20

14 0

5:41

:20.

View Article Online / Journal Homepage / Table of Contents for this issue

NICHOLLS: MANNICH'S METHOD FOR THE DETERMINATION OF MORPHINE 441

to ensure the correct degree of alkalinity. In addition, with pure morphine the conditions specified by Mannich did not yield quantitative results, the solubility of the ether being approximately 4 mg. per 100 ml.

The method, however, appeared sufficiently promising to warrant further study, and it was found that when the precipitation was carried out in about 30 per cent. ethyl alcohol solution (instead of in aqueous methyl alcohol) and a considerable quantity of ammonia (instead of fixed alkali) was used, quantitative results could be obtained with very little, if any, decomposition of the reagent.

APPLICATION OF THE MODIFIED METHOD TO MORPHINE SALTs.-Solutions containing known amounts of pure morphine dissolved in N/10 acid were diluted with water to 60 ml., and 25 ml. of alcohol (95 per cent.), 10 ml. of strong ammonia solution and 5 ml. of a 2 per cent. solution of 1 :chloro-2:4-dinitrobenzene in alcohol (95 per cent.) were added to each and well mixed. After standing overnight (18 hours) each was filtered through a tared Gooch crucible packed with asbestos, the precipitate and flask being washed with 30 per cent. alcohol and finally with a little ether to remove any traces of chlorodinitrobenzene. The crucible was dried at 100" C. and weighed. The results obtained are given in the following table:

Anhydrous morphine

present g-

0-07 16 0.0294 0.0029 0.00074

Anhydrous Weight of ether morphine

obtained (ether x 0.632) g* g-

0-1132 0.0464 0.0046 0.0012

0.0716 0.0293 0-0029 0.00076

With greater concentrations of morphine, precipitation was not complete in 18 hours, possibly owing to insufficient excess of chlorodinitrobenzene. The quantity of this reagent that can be usefully added is limited by its solubility in the 30 per cent. alcoholic solution.

The conditions applicable to morphine salts may be summarised as follows:- Dissolve a weighed quantity of the morphine salt in 30 per cent. alcohol. To every 100 ml. of solution, which must not contain more than 0.1 g. of morphine salt, add 10 ml. of strong ammonia solution and 5ml. of a 2 per cent. solution of 1 :2:4-~hlorodinitrobenzene in alcohol (95 per cent.). Allow the mixture to stand for 18 hours, filter through a tared Gooch crucible, and wash the precipitate with 30 per cent. alcohol and finally with a little ether. Dry the precipitate a t 100" C. and weigh. Multiply the weight of the precipitate by 0.632 to obtain anhydrous morphine.

These conditions can be employed for certain mixtures containing morphine salts; but it must be remembered that other phenolic alkaloids may give insoluble ethers with chlorodinitrobenzene.

APPLICATION TO OPIuM.-It was found that opium extracts, prepared as described by Mannich and precipitated under the modified conditions given above, yielded precipitates of different colour from those given by morphine salts, the shades varying from yellow to brown. An additional small error was introduced by the fact that after precipitation of the calcium from the lime water extract of

Publ

ishe

d on

01

Janu

ary

1937

. Dow

nloa

ded

by U

nive

rsity

of

Prin

ce E

dwar

d Is

land

on

31/1

0/20

14 0

5:41

:20.

View Article Online

442 NICHOLLS : MANNICH’S METHOD FOR THE DETERMINATION OF MORPHINE

opium by means of potassium oxalate the addition of the necessary alcohol yielded a further small precipitate of calcium oxalate. The former of these difficulties was overcome by treating the opium extracts with lead acetate, and the latter by precipitating the calcium in 30 per cent. alcoholic solution. A convenient treatment of opium was as follows:

Two or five g. of opium were completely extracted with successive portions of water, and the solutions were filtered through a sintered glass funnel and diluted to 100 or 250ml., respectively. To 75ml. of the solution were added O G g . of powdered lead acetate and, when this had dissolved, 0-5 g. of calcium hydroxide, and the mixture was well shaken and filtered through a fluted filter-paper. To 50 ml. of the filtrate (equivalent to 1 g. of opium) were added 1 g. of oxalic acid and 30 to 35ml. of alcohol (95 per cent.) and the mixture was allowed to stand for an hour and then diluted to 100ml. with water. After filtration, an aliquot part of the filtrate was treated as specified above.

Alternatively, 1 g. of opium was ground into a sludge with 0-5 g. of lead acetate and a little water, and then mixed with 0-5 g. of calcium hydroxide. The mixture was filtered on a sintered glass funnel, and the residue was re-ground with water and filtered. The process was repeated until the opium was completely extracted, yielding about 80 ml. of filtrate. To the filtrate were added 1 g. of oxalic acid and sufficient alcohol to yield approximately 30 per cent. in the solution. After being shaken and allowed to stand, the mixture was filtered, and the residue was washed with 30 per cent. alcohol. An aliquot part of the filtrate was treated in the same way as for morphine.

In every instance several tests were carried out with the same volume of solution for precipitation, but with varying concentrations of opium extract. It was found that the smaller concentrations gave lower results than the larger, not on account of solubility, but owing, a t least in part, to a slower rate of precipitation; if the mixtures were allowed to stand for longer than 18 hours, in some cases 4 days, the results were approximately the same. Examination of the precipitates showed, however, that they were not the pure morphine ether; when tested by Zeisel’s method they all yielded silver iodide, indicating the presence of methoxy groups, which are not present in morphine. The weights of silver iodide obtained from 0.1 g. of ethers derived from different varieties of opium varied from 0.0012 to 0-0077 g. Ethers obtained from opium extracts from which the non- phenolic alkaloids had been exhaustively extracted still contained methoxy groups, showing that other phenolic alkaloids in opium give insoluble ethers in the same way as morphine. Assuming that these interfering alkaloids contain, like laudanine, three methoxy groups, the morphine calculated from the weight of ether produced may be up to 6 per cent. too high, 2.e. 0.6 per cent. on 10 per cent. of morphine. If the interfering alkaloids have one or two, instead of three, methoxy groups, the error is proportionately greater.

The Mannich method is, therefore, unsatisfactory for the accurate assay of opium.

SUMMARY.-~. Mannich’s method has been modified to give quantitative results for the assay of morphine in its salts.

Publ

ishe

d on

01

Janu

ary

1937

. Dow

nloa

ded

by U

nive

rsity

of

Prin

ce E

dwar

d Is

land

on

31/1

0/20

14 0

5:41

:20.

View Article Online

ISMAIL AND HARWOOD: THE DETERMINATION OF POTASSIUM 443

2. The method, whether modified or not, does not give accurate results with opium, since other phenolic alkaloids present in opium yield insoluble ethers under the same conditions.

I wish to thank Dr. J. J. Fox, Government Chemist, for permission to publish this work.

REFERENCE 1. C. Mannich, K. Handke and G. Baumgarten, Arch. Pharm., 1935, 273, 97.

GOVERNMENT LABORATORY LONDON, W.C.2

Publ

ishe

d on

01

Janu

ary

1937

. Dow

nloa

ded

by U

nive

rsity

of

Prin

ce E

dwar

d Is

land

on

31/1

0/20

14 0

5:41

:20.

View Article Online