m and Rz%=cr~s 1 (1980) 161-16,

Research Note

Substituted Benzylidene Cyanides

B-N JHA

Depamnent of Chemrstry, S.P College (Bhagalpur Unzuersl@), Dumka (S P)-814101. Bthar, Indta

and

J CBANEIRJI

Dcpamnent of Chemlshy, B N College. Puma Unwers~ry, Puma-800004, Bzhar. Kndla

SUMMARY

Eight new chain substttuted benzylidene cyanine dyes have been prepared by condensing 4-dimethylamino-2’-nitrobenzophenone and 4-drmethylamzno-3’S’-

dmitrobenzophenone with methiodides of quinaldine and 6_haloquinaldines, m

absolute ethanol, using pipen’dine as a basic catalyst. The optical absorption and

extra sensltisation data of the dyes have been recorded and compared with those

of their methin analogues.

The dyes absorb at longer wavelengths than thezr unsubstituted analogues,

contrary to earlier observations.‘d The dyes obtained from the 2’-nitroketone are good sensitisers, whereas those obtained from the 3’,5’-dinitroketone, are densen-

sitisers

1. tN-l-R3DUCTION

Although quite a large number of 4-dialkylamino styryl dyes, containing different variously substituted heterocyclic nuclei are reported, and the effect on optlcal absorption and sensitisation of substituents in the hetero part of ‘rhe hemicyanines has been extensively studied,’ very little work has been carried out to study the effect of substituents in the methin chain of the dye mo1ecules.8-” Moreover, Q!- and p-methin substitutions in styryl cyanines are reported to cause a hypsochromic shift in the absorption maxima, when compared to their unsubstituted analogues,‘-3 but the extent of the hypso- chromic shift is less pronounced in the case of P-substituted products.- It was

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162 B N JHA J CBANEtRIl

therefore of interest to prepare some ,G-methin substituted styryi cyanines and study thetr opttcal properties systematically_

The p-methtn chain substitution can be effected by using suitable I-p- dtalkylamino ketones in place of 4-p-dialkylaminoaldehydes

This paper reports the preparation of dyes denved from two ketones, 4- dimethylamino-2’-nitrobenzophenone and 4-dimethylamtno-3’.5’-dmitro- benzophenone. whtch were obtained by the method of Shah er al.” with suttable modificattons. The quatemtsed bases required, were prepared by heating the base with methy iodide-l3 The synthesised ketones were separately condensed rn the usual waylJ wtth methtodtdes of qutnaldine” and 6-chloro-. 6-bromo- and 6-iodoqutnaldinest3 I6 tn absolute ethanol in the presence of a few drops of ptperidtne to afford etght new dyes (II),,-D2,) as in Scheme 1

The dyes (D,,-D,,) obtained from 4-dtmethylamtno-2’-nttrobenzophenone and dyes (D3, -DZ2) from 4-dimethylamtno-3’.5’-dinttrobenzophenone are htghly crystalline and are mostly dark vrolet m colour. Then- alcoholtc soluttons are either reddish vtolet or violet The colour is reverstbtly dtscharged by addttion of mtneral actds and regenerated on bastficatton, indtcsttve of the charactensttc of cyantne dyes

,!3-Methrn substttutton may affect the resonance stabiltsatron of substttuted dye molecules stertcally and electrontcally. as the substituents under study are electron attracttng. The stenc htndrance to resonance tn the matn conjugated chatn due to bulkrness of the substttuents IS hkely to be significant too.

The data for optical absorptton maxima and the ranges of extra sensttisation have been recorded. analysed and compared wtth those of their corresponding styryl analogues wherever posstble and reasonable conclusions have been drawn.

2 covcJ-us10ss

The absorptton ma\tma and extra senstttsatton of the newly prepared dyes and those of thetr styryl analogues. available tn the literature. are shown tn Table 1 for comparison.

It ~111 be evident from the absot-ptton data that P-methtn substttutton, whether by 2-nttrophenyl or by 3.5-dtnitrophenyl, has caused an almost untform bathochromtc shift in A,,, by about 30 rnp. It will also be seen that 6-substttution of the heteronucleus has caused only a slight bathochromic shift

tn A,,. the order being 6-H < 6-CI < 6-Br < 6-I tn both the 2-nitro senes and the 3.5dmicro sertes Analysts of the sensittsation data. however, does not lead to any definite generalisation The p-2-nitrophenyl dyes are inferior sensitisers to their unsuhstttuted analogues. while the P-3.5-dtmtrophenyl dyes are desen- sittsers

163

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TABLE 1 THE RECORDED DATA OF ABSORPTION M/U5MA (h,,) AND ECl-R4 SENSll-ISAl-ION OF THE

BENZYUDENECYANlNE DYES AND -l-HOSE OF IJN- TITRYL ANALOGUES

Subsntured benzylrdene Unsubshtuted styryl dyes cyanme dyes Cfrom rhe Lferufure)

Extra sensrfrsanon Exfra sensNzsatzon

range klU.S range

(mw) (mw) her) Reference

D,,

D,, D,, D 2” D,, D 71 D h D 14

56.4 620 w. 560 530 680 580 11 dc, lbvr

578 630 nu, c 590 u 548 650 595 16 579 630 rm. c 590 550 650 595 16 583 650 I, Ic 590 552 650 600 16 569 Da - 530 680 580 11 578 Da - 548 650 595 16 580 D” - 550 650 595 16 583 Da - 552 650 600 16

Abbreomrroru c connected. I Intense, u unpronounced. w weak, dc &sconnected. Ic loosely connected, ml moderately Intense lbvr Intense In blue-violet range, D desenslt- ,ser a In all cases, lntenslty m blue-violet range IS decreased The desenslhsmg properry vanes En the order D,,CD,,<D,,<D,,

3. ECXPEFUhfJ3J-l-AL

3.1. TIze ketones

For the preparation of ketones, the general method of production of alkyl- amrnobenzophenones and therr substituted products by Shah et al.” was

adopted wrth some procedural modifications.

(I) 4-Dimethylamino-2’-mtrobenzophenone: Dtmethylanihne (8 ml) was added in portions to a mixture of o-nitrobenzanihde (3g) and phosphorus oxychloride (8 ml) and warmed (4045°C) for 8 h. The viscous mass, on extracting with hydrochlonc acid, was almost neutralised with sodium hydrox- ide solution and rendered homogeneous with alcohol. The ketone, which separated after additton of a few drops more of sodium hydroxtde solution and chilling, was recrystallised from toluene as shining deep orange leaflets (yield 30%. m p. 24%50°C; ref. 12. yield not mentioned, m-p. 251-53°C).

(ii) 4-Dimethylamlno-3’,5’-dmltrobenzophenone: 3,5-Dinitrobenzanilide (5 g) and dimethylanihne (7 ml) were mixed together and phosphorus oxych- loride (7 ml) was slowly added. The mixture was heated on a steam bath for

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6 h and then on an oil bath (115-120°C) for a further 4 h. The acid extract of the crude product was neutralised with sodium hydroxide solution and the separated ketone recrystallised from a mixed solvent, ethanol: benzene (3: l), as light orange coloured shining woolly crystals, (yield 40%, m-p. 193-94°C).

Found: C, 57-11; H. 4-06; N. 13-28%

C,sH,,NL& requires: C. 57- 14: H, 4-14: N, 13.33%

3.2. Tile quaternary quinaldmlum salts

The quaternised salts were obtamed by adoptmg the general method of preparation of Johnson and Adams.‘3 The bases and methyl iodide (1: l-5 M) were heated In a pressure bottle on a steam bath for 24 h and the product recrystallised from hot water.

3 3. The benzyhdene cyatlrne dyes A nuxture, contaming requlslte amounts of the ketone, the quatemary salt.

ethanol and a few drops of piperidlne was refluxed mildly under a moisture trap for about 2 h The resulting solution. on cooling. afforded the dye. which was recrystalllsed from methanol

The percentage analysis. yield. m p (uncorrected). etc of the dyes are given In Table 2

3.-I Recordttlg of opucal properrres

The absorption maxlma of the dyes were recorded on an Beckmann Spec- trophotomerer. Model DU In l/1000 ethanolic solutions. The sensitlsatlon spectra were recorded on an Adam Hllger Wedge Spectrograph on Ilford N40 process plates, bathed In dilute ethanol (1 _ 3) solutions (l/50 000) of dyes. The plates after -t min bathing were dried. exposed for 4 mm to light from a 150 c-p point-o-hte lamp

AChNOWLEDGEblENTS

The authors wish to thank Dr A K. Slnha, Reader In Chemistry. B. N. College. Patna-SO0004 for his support during this investigation

FCEFEFZENCES

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3- I K USHENKO Ukr k’l;m 211 . 20, 3SI (1954). Chem Absr . 50, 6019 (1956) 3 I K USHLYKO CJhr AIhrm 211 21, 73s (1935). Chetn Absr , 50, 16752 (1956)

4 I G FAFZBEN. Bnt Pat 495. 012 5. A I KIPFUANOV and I. K USHENKO. J Gem Chem US S R , 20, 514, Enghsh translation,

543 (1950) 6 F. M TIER. J. Chem Sot, 1480 (1956) 7. F. M HAMER. Cvanine dves and related comuounds New York. InterscIence Pubhshers Inc

(1964) G~\es a ~omprehdnswe surxey of the subject covered by this paper 8 W H. Mrus and J L B SMITH. J Chem Sot , 121, 2724 (1922) 9 JCB ANEIUI. K. D. B-, N P BHATTACHARYA and S N SANYAL. J. Indian Chem

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