)joebxj1vcmjtijoh$psqpsbujpo +pvsobmpg$ifnjtusz …

Research ArticleTwo New 1133-Tetramethylguanidinium Halochromates(C5H14N3CrO3X) (X Cl F) Efficient Reagents forOxidation of Organic Substrates under Solvent-FreeConditions and Microwave Irradiation

KJvJlcJm FendJl1 H Beytiye Oumlzguumln2 and Ebru Uumlstuumln2

1Department of Chemistry Faculty of Science Kafkas University 36100 Kars Turkey2Department of Chemistry Faculty of Science Gazi University 06100 Ankara Turkey

Correspondence should be addressed to Kıvılcım Sendıl kivilcimsendilhotmailcom

Received 27 January 2016 Revised 27 March 2016 Accepted 11 April 2016

Academic Editor Cristina Femoni

Copyright copy 2016 Kıvılcım Sendıl et alThis is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Two new mild oxidizing agents 1133-tetramethylguanidinium fluorochromate (TMGFC) and 1133-tetramethylguanidiniumchlorochromate (TMGCC) were prepared in high yields by reacting tetramethylguanidine with CrO

3and related acid These

reagents are suitable to oxidize various primary and secondary alcohols and oximes to the corresponding carbonyl compoundsunder solvent-free conditions and microwave irradiation

1 Introduction

Oxidation of various organic compounds under mild condi-tions is of great importance in synthetic organic chemistry[1] Chromium(VI) is the most widely employed amongoxidizing agents based upon higher-valent transition metaloxo derivatives such as reagents derived from rutheniumosmium manganese and vanadium Since the appearanceof Collins reagent [2] significant improvements are achievedin the development of new Cr(VI) based oxidizing agentsfor the effective and selective oxidation of organic substratesin particular alcohols under mild conditions Some of theimportant entries in the list of reagents are pyridiniumchlorochromate (PCC) [3] pyridinium dichromate (PDC)[4] pyridinium fluorochromate (PFC) [5 6] quinoliniumfluorochromate (QFC) [7] 1133-tetramethylguanidiniumdichromate (TMGDC) [8] quinolinium chlorochromate(QCC) [9] and 35-dimethylpyrazolium fluorochromate(DmpzHFC) [10] However the chromium based reagentsthat have been developed so far have some limitations thatcannot be overlooked These include the inherent problemsof acidity of the reagents instability tedious work-up a long

reaction time overoxidation use of toxic solvent or a needfor excess amount of reagent [11ndash18] Consequently there isstill scope for the search of highly efficient andmild oxidizingagents

Recently considerable attention has been paid to solvent-free reactions [19] These reactions not only are of interestfrom an ecological point of view but in many cases also offerconsiderable synthetic advantages in terms of yield selectiv-ity and simplicity of the reaction procedure In recent yearsorganic reactions assisted by microwave irradiation havegained special attention [20] Microwave assisted organictransformations coupled with solvent-free conditions haveattracted much attention due to enhanced reaction rateseasier work-up and facilitated purification [21ndash24]

In continuation of our ongoing research program for de-veloping newer chromium reagents [25ndash28] two new oxi-dizing agents such as 1133-tetramethylguanidinium fluo-rochromate (TMGFC) and 1133-tetramethylguanidiniumchlorochromate (TMGCC) shown in Figure 1 were synthe-sized with the belief that these reagents could be used for theoxidation of organic substrates

Hindawi Publishing CorporationJournal of ChemistryVolume 2016 Article ID 3518102 7 pageshttpdxdoiorg10115520163518102

2 Journal of Chemistry

C N C N CrF

OO

TMGCC TMGFC

CrCl

OO

H

H+

H

H+minusO minusO

(H3C)2N

(H3C)2N

(H3C)2N

(H3C)2N

Figure 1

2 Experimental

All reagents and solvents were obtained from Aldrich andused without further purification The 1H NMR spectrumwas recorded on a Bruker Avance 300-MHz spectrome-ter (Germany) Elemental analysis was performed usingan Elemental Micro Vario CHNS Electrothermal meltingpoints were determined by a 9200 digital melting pointapparatus (United Kingdom) and are uncorrected IR spectrawere recorded on a Mathson 1000 FT-IR spectrometerAll microwave irradiation reactions were carried out on aMilestone Micro-Synth apparatus

21 Preparation of 1133-TetramethylguanidiniumFluorochro-mate (TMGFC) Chromium(IV)oxide (CrO

3) (20mmol 2 g)

was taken in a polyethylene beaker and 48 hydrofluo-ric acid (HF) (23mmol 11mL) was added dropwise withcontinuous stirring for 10min The orange solution thusobtained was cooled in an ice-bath To this solution 1133-tetramethylguanidine (20mmol 25mL) was added portion-wise in 15min The mixture was kept at minus10∘C for 1 hourThe orange amorphous solid thus formed was filtered offwashed twice with hexane and dried under vacuum for1 h Yield 85 mp 130-131∘C 1H NMR (300MHz DMSO-d6) 120575 = 29 (s 3H) 120575 = 778 (s 2H -NH

2) IR (KBr)

] = 951 cmminus1 (Cr=O) 771 cmminus1 (Cr=O) 539 cmminus1 (Cr-F) Elemental Analysis (C

5H14N3CrO3F) (Calculated) 2553

(C) 596 (H) 1794 (N) (Found) 2616 (C) 649(H) 1814 (N)

22 Preparation of 1133-Tetramethylguanidinium Chloro-chromate (TMGCC) Chromium(IV)oxide (CrO

3) (20mmol

2 g) was taken in a polyethylene beaker and 6M hydrochloricacid (HCl) (20mmol 36mL) was added dropwise withcontinuous stirring for 10min The orange solution thusobtained was cooled in an ice-bath To this solution 1133-tetramethylguanidine (20mmol 25mL) was added portion-wise in 15min The mixture was kept at minus10∘C for 1 hourThe orange amorphous solid thus formed was filtered offwashed twice with hexane and dried under vacuum for1 h Yield 75 mp 136-137∘C 1H NMR (300MHz DMSO-d6) 120575 = 29 (s 3H) 120575 = 775 (s 2H -NH

2) IR (KBr)

] = 951 cmminus1 (Cr=O) 778 cmminus1 (Cr=O) 458 cmminus1 (Cr-Cl)Elemental Analysis (C

5H14N3CrO3Cl) (Calculated) 2390

(C) 558 (H) 1673 (N) (Found) 2499 (C) 562(H) 1685 (N)

23 General Procedure for the Oxidation under Solvent-FreeConditions The oxidant (15ndash2mmol) was added to the sub-strate (1mmol) in a mortar Starting materials were instantly

mixed ground and kept for the appropriate period at roomtemperature or in an oven without any further agitation Theprogress of the reactionwasmonitored by using TLC on silicagel (benzene ethyl acetate = 9 1) Upon completion of thereaction extraction with ether (3 times 25mL) and evaporationof the solvent gave the corresponding carbonyl compounds

24 General Procedure for the Oxidation under MicrowaveIrradiation The substrate (1mmol) and 15ndash2mmol oxidantwere mixed To this mixture 05mL CH

2Cl2was added The

mixture was subjected to microwave irradiation (1000W)Upon completion of the reaction extraction with ether (3 times25mL) and evaporation of the solvent gave the correspondingcarbonyl compounds The products formed were analyzedby their 24-dinitrophenylhydrazone derivatives The precip-itated 24-DNP was filtered off weighed and recrystallizedfrom ethanol

3 Results and Discussion

1133-Tetramethylguanidinium fluorochromate (TMGFC)and 1133-tetramethylguanidinium chlorochromate(TMGCC) can easily be prepared in good yields by reactingtetramethylguanidine with CrO

3and related acid at a molar

ratio of 1 1 1 in aqueous mediumTMGFC and TMGCC are orange colored stable amor-

phous solids at room temperature They are moisture insen-sitive and can be stored in polyethylene containers for longperiods without decomposition

The pH values of 001M aqueous solutions of PCC PFCTMGFC and TMGCC were found to be 175 245 379and 389 The higher pH values of TMGFC and TMGCCcompared to their companion reagents attest to their far lesspronounced acidic characters So TMGFC and TMGCCmaybe proper oxidizing agents for the oxidation of acid-sensitivecompounds

TMGFC and TMGCC are highly soluble in DMF andDMSO slightly soluble in acetonitrile and dichloromethaneand insoluble in benzene ether chloroform and tolueneThese results are indicative of the ionic nature of the reagents

The conductivity values of 10minus3M solutions of TMGFCand TMGCC in acetonitrile at 25∘C were found as140Ωminus1cm2molminus1 and 150Ωminus1cm2molminus1 respectivelySo they are 1 1 electrolytes

The effect of substrate oxidant molar ratios has beeninvestigated by applying 1 1 1 125 1 15 and 1 2 molarratios respectively for the oxidation of benzyl alcohol asa model substrate under solvent-free conditions at roomtemperature for 30min The yields thus obtained were givenin Table 1

Journal of Chemistry 3

OH

TMGFC or TMGCCSolvent-free rt

O

NOH

or MW

R1

R1

R1

R2

R2

R2

R1 R2 alkyl aryl allyl and H

Scheme 1

Cr

X

OOH

H

H

+ O

H

H

Cr

O X

+O NC

H HH

+

Proton transfer

O

H

H

Cr

HO

O X

+NC

H HO

H

H

CrHO

O

O

CH

O + CrO

HO OH

+NC

H H

+NC

H H+

X = F Cl

R998400

Xminus

Xminus

(H3C)2N

(H3C)2N

(H3C)2N

N(CH3)2

N(CH3)2

N(CH3)2

R998400R998400

Ominus

Ominus

OminusR998400

N(CH3)2(H3C)2N

R998400

Ominus

Scheme 2

Table 1 Oxidation of benzyl alcohol with different amounts ofTMGCC and TMGFC

Oxidants Substrate oxidants (molar ratio) Yielda

TMGCC

1 1 721 125 741 15 801 2 86

TMGFC

1 1 751 125 781 15 851 2 90

aYields refer to the isolated 24-DNP derivative [29]

To show the influence of nature of solvent on the reactivityof the oxidants various solvents such as CH

2Cl2 acetone and

DMF have been used for the oxidation of benzyl alcohol asrepresentative substrate (Table 2)

The use of more polar solvents such as DMF and acetoneresulted in moderate yields

Table 2 Oxidation of benzyl alcohol in different solvents withTMGCC and TMGFC

Solvents Substrate oxidation(molar ratio)

Reactionperiodh

TMGCCYielda

TMGFCYielda

CH2Cl2 1 2 2 82 88

Acetone 1 2 2 63 70DMF 1 2 2 60 65aYields refer to the isolated 24-DNP derivative [29]

In order to ascertain the efficiency of the reagents asoxidants different types of primary and secondary alcoholsand oximes were treated with the reagents by taking themolar ratio of substrate oxidant as 1 1-2 under solvent-free conditions at room temperature and under microwaveirradiation to afford the corresponding carbonyl compounds(Scheme 1)

A probable mechanism for the oxidation with TMGCCand TMGFC is given on the basis of previously reportedmechanisms [30] (Scheme 2)


Table 3 The oxidation of alcohols and oximes with TMGFC under solvent-free conditions at room temperature and under microwaveirradiation

Entry Substrate ProductYield (time)a

Solvent-free(hour)

Microwave(second)

1 CH3(CH2)6CH2OH CH

3(CH2)6CHO 76 (4) 77 (10)

2 OH(H3C)3C O(H3C)3C 70 (4) 75 (13)

3 OH O 75 (35) 76 (13)

4HO

CH3

O

CH370 (4) 75 (10)

5 CH=CHCH2OH CH=CHCHO 85 (05) 90 (5)

6 CH2OH CHO 90 (05) 92 (4)

7 MeO CH2OH CHOMeO 90 (1) 93 (7)

8 CH2OH CHO 85 (1) 89 (8)

9 Cl CH2OH CHOCl 86 (1) 92 (9)

10 CH2OHO2N CHOO2N 87 (125) 88 (10)

11 HCC

O

HOCO

CO

42 (45)(70∘C) 60 (10)

12HC

OH

C

O85 (1) 85 (8)

13 Benzoin oxime Benzoin 55 (8) 58 (10)14 Cyclohexanone oxime Cyclohexanone 70 (4) 75 (20)15 Cyclopentanone oxime Cyclopentanone 70 (7) 78 (10)aYield was based on 24-dinitrophenylhydrazone derivative identified by melting point [29] (except for the 4-nitrobenzaldehyde and benzil whose meltingpoints were taken directly)

Primary benzylic alcohols and 1-octanol were convertedinto their corresponding aldehydes with good to high yields(Tables 3 and 4 entries 1 and 6ndash10) The oxidation of thesealcohols is performed devoid of overoxidationThe reactivityof the aliphatic primary and secondary alcohols seemed to beslightly lower than benzylic alcohols (Tables 3 and 4 entries1ndash4) It is also noteworthy that cinnamyl alcohol (Tables 3and 4 entry 5) was converted to cinnamaldehyde withoutthe cleavage of the benzylic double bond and the reaction isessentially chemoselective

Aliphatic oximes such as cyclohexanone oxime and cyclo-pentanone oximewere deoximatedmore efficiently than ben-zoin oxime (Tables 3 and 4 entries 13ndash15) The oxidation

reactions of polycyclic aromatic hydrocarbons such as an-thracene and phenanthrene were attempted by taking themolar ratio of substrate oxidizing agent as 1 3 undermicrowave irradiation but the substrates remained intact

During the reactions the color of the oxidants changesfrom orange to brown providing visual means for ascertain-ing the progress of the oxidation

In order to show the oxidative ability of the reagents(TMGCC and TMGFC) we compared some of our resultswith those of PCC [20] PFC [31 32] BAAOC [33] andDmpzHFC [34] carried out under solvent-free conditions(Table 5)


Table 4 The oxidation of alcohols and oximes with TMGCC under solvent-free conditions at room temperature and under microwaveirradiation


Solvent-free(hour)

Microwave(second)

1 CH3(CH2)6CH2OH CH

3(CH2)6CHO 70 (45) 74 (11)

2 OH(H3C)3C O(H3C)3C 75 (4) 75 (15)

3 OH O 75 (35) 73 (14)

4HO

CH3

O

CH372 (5) 73 (10)


6 CH2OH CHO 85 (1) 90 (7)


8 CH2OH CHO 80 (2) 85 (11)

9 Cl CH2OH CHOCl 85 (15) 84 (10)

10 O2N CH2OH CHOO2N 86 (15) 85 (11)

11 HCC

O

HOCO

CO

40 (6)(70∘C) 50 (10)

12HC

OH

C

O82 (1) 86 (10)


Table 5 Comparison of oxidation of various organic substrates by TMGCC TMGFC PCC PFC BAAOC and DmpzHFC

Yield (time [min])Substrate TMGCC TMGFCC PCC [20] PFC [31 32] BAAOC [33] DmpzHFC [34]4-Methoxybenzyl alcohol 91 (1) 90 (1) 94 (5) 89 (10) 99 (2) 92 (2)4-Chlorobenzyl alcohol 85 (15) 86 (1) 93 (10) 78 (10) 95 (7) mdashBenzyl alcohol 85 (1) 90 (05) 96 (15) 93 (10) 98 (1) 85 (1)Cinnamyl alcohol 85 (1) 85 (05) 95 (15) 85 (10) 85 (20) 89 (2)

4 Conclusion

In conclusion we have developed two new reagents TMGFCand TMGCC for the oxidation of alcohols and oximes We

described a solvent-free and a highly efficient microwaveinduced procedure for the rapid synthesis of aldehydes andketones These transformations enjoy the chemical and envi-ronmental advantages of solvent-free reactions The results


obtained are satisfactory and show the new reagents to bevaluable additions to the existing agent

Competing Interests

The authors declare that they have no competing interests

References

[1] F A Luzzio and F S Guziec ldquoRecent applications of oxo-chromiumamine complexes as oxidants in organic synthesis Areviewrdquo Organic Preparations and Procedures International vol20 no 6 pp 533ndash584 1988

[2] J C Collins W W Hess and F J Frank ldquoDipyridine-chromium(VI) oxide oxidation of alcohols in dichlorometh-anerdquo Tetrahedron Letters vol 9 no 30 pp 3363ndash3366 1968

[3] E J Corey and J W Suggs ldquoPyridinium chlorochromateAn efficient reagent for oxidation of primary and secondaryalcohols to carbonyl compoundsrdquo Tetrahedron Letters vol 16no 31 pp 2647ndash2650 1975

[4] E J Corey andG Schmidt ldquoUseful procedures for the oxidationof alcohols involving pyridinium dichromate in aprotic mediardquoTetrahedron Letters vol 20 no 5 pp 399ndash402 1979

[5] M N Bhattacharjee M K Chaudhuri H S Dasgupta N Royand D T Khathing ldquoPyridinium fluorochromate a new andefficient oxidant for organic substratesrdquo Synthesis vol 1982 no7 pp 588ndash590 1982

[6] M N Bhattcharjee M K Chaudhuri and S PurkayasthaldquoSome aspects of pyridinium fluorochromate C

5H5NHCrO

3F

(PFC) oxidations stoichiometry of oxidation of alcoholsevidence for oxygen transfer and the identity of the reducedchromium speciesrdquo Tetrahedron vol 43 no 22 pp 5389ndash53921987

[7] M K Chaudhuri S K Chettri S Lyndem P C Paul andP Srinivas ldquoQuinolinium fluorochromate (QFC) C

9H7NH

(CrO3F) an improved Cr(VI)-oxidant for organic substratesrdquo

Bulletin of the Chemical Society of Japan vol 67 no 7 pp 1894ndash1898 1994

[8] S Goswami and A Kar ldquoGuanidinium chlorochromate anew efficient and mild oxidizing agent for benzylic and otheralcohols to carbonyl compounds in water and organic solventsrdquoSynthetic Communications vol 41 no 17 pp 2500ndash2504 2011

[9] R Srinivasan C V Ramesh W Madhulatha and K Balasub-ramanian ldquoOxidation of alcohols by quinolinium chlorochro-materdquo Indian Journal of Chemistry B Organic Chemistry includ-ing Medicinal vol 35B pp 480ndash481 1996

[10] U Bora M K Chaudhuri D Dey D Kalita W Khar-mawphlang and G C Mandal ldquo35-Dimethylpyrazolium flu-orochromate(VI) C

5H8N2H[CrO

3F] (DmpzHFC) a conve-

nient new reagent for oxidation of organic substratesrdquo Tetrahe-dron vol 57 no 12 pp 2445ndash2448 2001

[11] G Maier H P Reisenauer and M De Marco ldquoIsonitroso hy-drogen (hydroxy nitrene HON)rdquo Angewandte ChemiemdashInter-national Edition vol 38 no 1-2 pp 108ndash110 1999

[12] A Bhandari P K Sharma and K K Banerji ldquoKinetics andmechanism of the oxidative regeneration of carbonyl com-pounds from oximes by pyridinium chlorochromaterdquo IndianJournal of ChemistrymdashSection A Inorganic PhysicalTheoreticaland Analytical Chemistry vol 40 no 5 pp 470ndash474 2001

[13] S Meenakshisundaram and R Sockalingam ldquoKinetics andmechanism of the quinolinium fluorochromate oxidation of

some primary secondary and unsaturated alcohols in acetoni-trilerdquoCollection of Czechoslovak Chemical Communications vol66 no 6 pp 877ndash896 2001

[14] J H Clark S R Cullen S J Barlow and T W BastockldquoEnvironmentally friendly chemistry using supported reagentcatalystsmdashstructure-property relationships for clayzicrdquo Journalof the Chemical Society Perkin Transactions 2 no 6 pp 1117ndash1130 1994

[15] R S Varma R Dahiya and R K Saini ldquoIodobenzene diacetateon alumina rapid oxidation of alcohols to carbonyl compoundsin solventless system using microwavesrdquo Tetrahedron Lettersvol 38 no 40 pp 7029ndash7032 1997

[16] J-D Lou L-H Zhu L-L Pan L Li F Li and C-L GaoldquoSolventminusfree oxidation of secondary alcohols with chromiumtrioxiderdquo Synthesis and Reactivity in Inorganic Metal-Organicand Nano-Metal Chemistry vol 36 no 7 pp 585ndash587 2006

[17] J-D Lou and L-Z Wang ldquoAn efficient and selective solvent-free oxidation of alcoholsrdquo Chemical Papers vol 57 no 2 pp136ndash137 2003

[18] M Tajbakhsh R Hosseinzadeh andM Sadatshahabi ldquoSynthe-sis and application of 26minusDicarboxy pyridinium fluorochro-mate as a new solidminusphase oxidantrdquo Synthetic Communicationsvol 35 no 11 pp 1547ndash1554 2005

[19] A Saffar-Teluri ldquoFast selective oxidation of alcohols undersolvent-free conditionsrdquo Research on Chemical Intermediatesvol 39 no 7 pp 3337ndash3343 2013

[20] P Salehi H Firouzabadi A Farrokhi and M GholizadehldquoSolvent-free oxidations of alcohols oximes aldehydes andcyclic acetals by pyridinium chlorochromaterdquo Synthesis no 15pp 2273ndash2276 2001

[21] K Tanaka and F Toda ldquoSolvent-free organic synthesisrdquo Chem-ical Reviews vol 100 no 3 pp 1025ndash1074 2000

[22] M M Kazem G Shahriare and I Hossein ldquoMicrowave-assisted oxidation of alcohols and polyarenes with cetyltrimeth-ylammonium bromochromaterdquo Chinese Journal of Chemistryvol 27 no 8 pp 1501ndash1504 2009

[23] J Einhorn C Einhorn F Ratajczak and J-L Pierre ldquoEfficientand highly selective oxidation of primary alcohols to aldehydesby N-chlorosuccinimide mediated by oxoammonium saltsrdquoJournal of Organic Chemistry vol 61 no 21 pp 7452ndash74541996

[24] L Ross A and D S Donald ldquoMagtrieve an efficient magnet-ically retrievable and recyclable oxidantrdquo Tetrahedron Lettersvol 38 no 22 pp 3857ndash3860 1997

[25] B Ozgun and K Sendil ldquoQuinoxalinium Fluorochromate(QxFC) a new and efficient reagent for the oxidation of alco-hols in solution under solvent-free conditions and microwaveirradiationrdquo Phosphorus Sulfur and Silicon and the RelatedElements vol 181 no 4 pp 959ndash964 2006

[26] B Ozgun A Yaylaoglu and K Sendil ldquo4-Benzylpyridiniumfluorochromate an efficient and selective oxidant for organicsubstratesrdquoMonatshefte fur Chemie vol 138 no 2 pp 161ndash1632007

[27] K Sendil and B Ozgun ldquoDipyrazinium Tri(fluorotrioxochro-mate) an efficient oxidant for organic substratesrdquo Monatsheftefur Chemie vol 137 no 12 pp 1529ndash1533 2006

[28] M Canbulat and B Ozgun ldquo35-Dimethylpyrazolium chloro-chromate(VI) an efficient reagent for solvent-free oxidation oforganic substratesrdquo Synthesis and Reactivity in Inorganic Metal-Organic and Nano-Metal Chemistry vol 42 no 5 pp 634ndash6372012


[29] Z Rapport Handbook of Tables for organic Compounds Identi-fication CRC Press Boca Raton Fla USA 3rd edition 1976

[30] E J Corey and D L Boger ldquoOxidative cationic cyclizationreactions effected by pyridinium chlorochromaterdquo TetrahedronLetters vol 19 no 28 pp 2461ndash2464 1978

[31] M K Chaudhuri S K Dehury S S Dhar and U B SinhaldquoThe economic synthesis of pyridinium fluorochromate (VI)C5H5NH[CrO

3] (PFC) and solvent-free oxidation of organic

substrates with PFCrdquo Synthetic Communications vol 34 no 22pp 4077ndash4087 2004

[32] K Sendil Synthesis and characterization of some oxochromdi-chromates halochromates investigation of oxidation reactionsof various organic compounds in different mediums [PhD the-sis] 2005 httpstezyokgovtrUlusalTezMerkezitezSorguSo-nucYenijsp

[33] A R Hajipour H R Bagheri and A E Ruoho ldquoSolidstate oxidation of alcohols using 1-butyl-4-aza-1-azoniabicy-clo[222]octane chlorochromaterdquo Bulletin of the Korean Chem-ical Society vol 25 no 8 pp 1238ndash1240 2004

[34] M K Chaudhuri S K Dehury S Hussain A Duarah andN Gogoi ldquoThe selective solid-phase oxidation of alcoholsand other organic substrates by 35-dimethylpyrazolium Flu-orochromaterdquo Organic Preparations and Procedures Interna-tional vol 38 no 3 pp 331ndash336 2006

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Applied ChemistryJournal of



Theoretical ChemistryJournal of


Journal of

Spectroscopy

Analytical ChemistryInternational Journal of


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Quantum Chemistry


Organic Chemistry International

ElectrochemistryInternational Journal of



CatalystsJournal of


C N C N CrF

OO

TMGCC TMGFC

CrCl

OO

H

H+

H

H+minusO minusO

(H3C)2N

(H3C)2N

(H3C)2N

(H3C)2N

Figure 1

2 Experimental

All reagents and solvents were obtained from Aldrich andused without further purification The 1H NMR spectrumwas recorded on a Bruker Avance 300-MHz spectrome-ter (Germany) Elemental analysis was performed usingan Elemental Micro Vario CHNS Electrothermal meltingpoints were determined by a 9200 digital melting pointapparatus (United Kingdom) and are uncorrected IR spectrawere recorded on a Mathson 1000 FT-IR spectrometerAll microwave irradiation reactions were carried out on aMilestone Micro-Synth apparatus

21 Preparation of 1133-TetramethylguanidiniumFluorochro-mate (TMGFC) Chromium(IV)oxide (CrO

3) (20mmol 2 g)

was taken in a polyethylene beaker and 48 hydrofluo-ric acid (HF) (23mmol 11mL) was added dropwise withcontinuous stirring for 10min The orange solution thusobtained was cooled in an ice-bath To this solution 1133-tetramethylguanidine (20mmol 25mL) was added portion-wise in 15min The mixture was kept at minus10∘C for 1 hourThe orange amorphous solid thus formed was filtered offwashed twice with hexane and dried under vacuum for1 h Yield 85 mp 130-131∘C 1H NMR (300MHz DMSO-d6) 120575 = 29 (s 3H) 120575 = 778 (s 2H -NH

2) IR (KBr)

] = 951 cmminus1 (Cr=O) 771 cmminus1 (Cr=O) 539 cmminus1 (Cr-F) Elemental Analysis (C

5H14N3CrO3F) (Calculated) 2553

(C) 596 (H) 1794 (N) (Found) 2616 (C) 649(H) 1814 (N)

22 Preparation of 1133-Tetramethylguanidinium Chloro-chromate (TMGCC) Chromium(IV)oxide (CrO

3) (20mmol

2 g) was taken in a polyethylene beaker and 6M hydrochloricacid (HCl) (20mmol 36mL) was added dropwise withcontinuous stirring for 10min The orange solution thusobtained was cooled in an ice-bath To this solution 1133-tetramethylguanidine (20mmol 25mL) was added portion-wise in 15min The mixture was kept at minus10∘C for 1 hourThe orange amorphous solid thus formed was filtered offwashed twice with hexane and dried under vacuum for1 h Yield 75 mp 136-137∘C 1H NMR (300MHz DMSO-d6) 120575 = 29 (s 3H) 120575 = 775 (s 2H -NH

2) IR (KBr)

] = 951 cmminus1 (Cr=O) 778 cmminus1 (Cr=O) 458 cmminus1 (Cr-Cl)Elemental Analysis (C

5H14N3CrO3Cl) (Calculated) 2390

(C) 558 (H) 1673 (N) (Found) 2499 (C) 562(H) 1685 (N)

23 General Procedure for the Oxidation under Solvent-FreeConditions The oxidant (15ndash2mmol) was added to the sub-strate (1mmol) in a mortar Starting materials were instantly

mixed ground and kept for the appropriate period at roomtemperature or in an oven without any further agitation Theprogress of the reactionwasmonitored by using TLC on silicagel (benzene ethyl acetate = 9 1) Upon completion of thereaction extraction with ether (3 times 25mL) and evaporationof the solvent gave the corresponding carbonyl compounds

24 General Procedure for the Oxidation under MicrowaveIrradiation The substrate (1mmol) and 15ndash2mmol oxidantwere mixed To this mixture 05mL CH

2Cl2was added The

mixture was subjected to microwave irradiation (1000W)Upon completion of the reaction extraction with ether (3 times25mL) and evaporation of the solvent gave the correspondingcarbonyl compounds The products formed were analyzedby their 24-dinitrophenylhydrazone derivatives The precip-itated 24-DNP was filtered off weighed and recrystallizedfrom ethanol

3 Results and Discussion

1133-Tetramethylguanidinium fluorochromate (TMGFC)and 1133-tetramethylguanidinium chlorochromate(TMGCC) can easily be prepared in good yields by reactingtetramethylguanidine with CrO

3and related acid at a molar

ratio of 1 1 1 in aqueous mediumTMGFC and TMGCC are orange colored stable amor-

phous solids at room temperature They are moisture insen-sitive and can be stored in polyethylene containers for longperiods without decomposition

The pH values of 001M aqueous solutions of PCC PFCTMGFC and TMGCC were found to be 175 245 379and 389 The higher pH values of TMGFC and TMGCCcompared to their companion reagents attest to their far lesspronounced acidic characters So TMGFC and TMGCCmaybe proper oxidizing agents for the oxidation of acid-sensitivecompounds

TMGFC and TMGCC are highly soluble in DMF andDMSO slightly soluble in acetonitrile and dichloromethaneand insoluble in benzene ether chloroform and tolueneThese results are indicative of the ionic nature of the reagents

The conductivity values of 10minus3M solutions of TMGFCand TMGCC in acetonitrile at 25∘C were found as140Ωminus1cm2molminus1 and 150Ωminus1cm2molminus1 respectivelySo they are 1 1 electrolytes

The effect of substrate oxidant molar ratios has beeninvestigated by applying 1 1 1 125 1 15 and 1 2 molarratios respectively for the oxidation of benzyl alcohol asa model substrate under solvent-free conditions at roomtemperature for 30min The yields thus obtained were givenin Table 1


OH


O

NOH

or MW

R1

R1

R1

R2

R2

R2


Scheme 1

Cr

X

OOH

H

H

+ O

H

H

Cr

O X

+O NC

H HH

+

Proton transfer

O

H

H

Cr

HO

O X

+NC

H HO

H

H

CrHO

O

O

CH

O + CrO

HO OH

+NC

H H

+NC

H H+

X = F Cl

R998400

Xminus

Xminus

(H3C)2N

(H3C)2N

(H3C)2N

N(CH3)2

N(CH3)2

N(CH3)2

R998400R998400

Ominus

Ominus

OminusR998400

N(CH3)2(H3C)2N

R998400

Ominus

Scheme 2



TMGCC

1 1 721 125 741 15 801 2 86

TMGFC

1 1 751 125 781 15 851 2 90



2Cl2 acetone and





Reactionperiodh

TMGCCYielda

TMGFCYielda

CH2Cl2 1 2 2 82 88







Solvent-free(hour)

Microwave(second)

1 CH3(CH2)6CH2OH CH

3(CH2)6CHO 76 (4) 77 (10)

2 OH(H3C)3C O(H3C)3C 70 (4) 75 (13)

3 OH O 75 (35) 76 (13)

4HO

CH3

O

CH370 (4) 75 (10)


6 CH2OH CHO 90 (05) 92 (4)


8 CH2OH CHO 85 (1) 89 (8)

9 Cl CH2OH CHOCl 86 (1) 92 (9)

10 CH2OHO2N CHOO2N 87 (125) 88 (10)

11 HCC

O

HOCO

CO

42 (45)(70∘C) 60 (10)

12HC

OH

C

O85 (1) 85 (8)










Solvent-free(hour)

Microwave(second)

1 CH3(CH2)6CH2OH CH

3(CH2)6CHO 70 (45) 74 (11)

2 OH(H3C)3C O(H3C)3C 75 (4) 75 (15)

3 OH O 75 (35) 73 (14)

4HO

CH3

O

CH372 (5) 73 (10)


6 CH2OH CHO 85 (1) 90 (7)


8 CH2OH CHO 80 (2) 85 (11)

9 Cl CH2OH CHOCl 85 (15) 84 (10)

10 O2N CH2OH CHOO2N 86 (15) 85 (11)

11 HCC

O

HOCO

CO

40 (6)(70∘C) 50 (10)

12HC

OH

C

O82 (1) 86 (10)




4 Conclusion





Competing Interests


References







5H5NHCrO

3F



9H7NH






5H8N2H[CrO








































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


OH


O

NOH

or MW

R1

R1

R1

R2

R2

R2


Scheme 1

Cr

X

OOH

H

H

+ O

H

H

Cr

O X

+O NC

H HH

+

Proton transfer

O

H

H

Cr

HO

O X

+NC

H HO

H

H

CrHO

O

O

CH

O + CrO

HO OH

+NC

H H

+NC

H H+

X = F Cl

R998400

Xminus

Xminus

(H3C)2N

(H3C)2N

(H3C)2N

N(CH3)2

N(CH3)2

N(CH3)2

R998400R998400

Ominus

Ominus

OminusR998400

N(CH3)2(H3C)2N

R998400

Ominus

Scheme 2



TMGCC

1 1 721 125 741 15 801 2 86

TMGFC

1 1 751 125 781 15 851 2 90



2Cl2 acetone and





Reactionperiodh

TMGCCYielda

TMGFCYielda

CH2Cl2 1 2 2 82 88







Solvent-free(hour)

Microwave(second)

1 CH3(CH2)6CH2OH CH

3(CH2)6CHO 76 (4) 77 (10)

2 OH(H3C)3C O(H3C)3C 70 (4) 75 (13)

3 OH O 75 (35) 76 (13)

4HO

CH3

O

CH370 (4) 75 (10)


6 CH2OH CHO 90 (05) 92 (4)


8 CH2OH CHO 85 (1) 89 (8)

9 Cl CH2OH CHOCl 86 (1) 92 (9)

10 CH2OHO2N CHOO2N 87 (125) 88 (10)

11 HCC

O

HOCO

CO

42 (45)(70∘C) 60 (10)

12HC

OH

C

O85 (1) 85 (8)










Solvent-free(hour)

Microwave(second)

1 CH3(CH2)6CH2OH CH

3(CH2)6CHO 70 (45) 74 (11)

2 OH(H3C)3C O(H3C)3C 75 (4) 75 (15)

3 OH O 75 (35) 73 (14)

4HO

CH3

O

CH372 (5) 73 (10)


6 CH2OH CHO 85 (1) 90 (7)


8 CH2OH CHO 80 (2) 85 (11)

9 Cl CH2OH CHOCl 85 (15) 84 (10)

10 O2N CH2OH CHOO2N 86 (15) 85 (11)

11 HCC

O

HOCO

CO

40 (6)(70∘C) 50 (10)

12HC

OH

C

O82 (1) 86 (10)




4 Conclusion





Competing Interests


References







5H5NHCrO

3F



9H7NH






5H8N2H[CrO








































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of




Solvent-free(hour)

Microwave(second)

1 CH3(CH2)6CH2OH CH

3(CH2)6CHO 76 (4) 77 (10)

2 OH(H3C)3C O(H3C)3C 70 (4) 75 (13)

3 OH O 75 (35) 76 (13)

4HO

CH3

O

CH370 (4) 75 (10)


6 CH2OH CHO 90 (05) 92 (4)


8 CH2OH CHO 85 (1) 89 (8)

9 Cl CH2OH CHOCl 86 (1) 92 (9)

10 CH2OHO2N CHOO2N 87 (125) 88 (10)

11 HCC

O

HOCO

CO

42 (45)(70∘C) 60 (10)

12HC

OH

C

O85 (1) 85 (8)










Solvent-free(hour)

Microwave(second)

1 CH3(CH2)6CH2OH CH

3(CH2)6CHO 70 (45) 74 (11)

2 OH(H3C)3C O(H3C)3C 75 (4) 75 (15)

3 OH O 75 (35) 73 (14)

4HO

CH3

O

CH372 (5) 73 (10)


6 CH2OH CHO 85 (1) 90 (7)


8 CH2OH CHO 80 (2) 85 (11)

9 Cl CH2OH CHOCl 85 (15) 84 (10)

10 O2N CH2OH CHOO2N 86 (15) 85 (11)

11 HCC

O

HOCO

CO

40 (6)(70∘C) 50 (10)

12HC

OH

C

O82 (1) 86 (10)




4 Conclusion





Competing Interests


References







5H5NHCrO

3F



9H7NH






5H8N2H[CrO








































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of




Solvent-free(hour)

Microwave(second)

1 CH3(CH2)6CH2OH CH

3(CH2)6CHO 70 (45) 74 (11)

2 OH(H3C)3C O(H3C)3C 75 (4) 75 (15)

3 OH O 75 (35) 73 (14)

4HO

CH3

O

CH372 (5) 73 (10)


6 CH2OH CHO 85 (1) 90 (7)


8 CH2OH CHO 80 (2) 85 (11)

9 Cl CH2OH CHOCl 85 (15) 84 (10)

10 O2N CH2OH CHOO2N 86 (15) 85 (11)

11 HCC

O

HOCO

CO

40 (6)(70∘C) 50 (10)

12HC

OH

C

O82 (1) 86 (10)




4 Conclusion





Competing Interests


References







5H5NHCrO

3F



9H7NH






5H8N2H[CrO








































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of



Competing Interests


References







5H5NHCrO

3F



9H7NH






5H8N2H[CrO








































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of



















Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of

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