2 . The synthesis oi 2,4,6,8-, of ~1,4,5,7-, and z ,4,5,8-1etramethyrl-qunrrol-illrac is dcseribed, and the properties of fhese base3 noted. ~'AST1INGfON.
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[b'QRTY-PlPTH
CONTRIlBUrlON EROM THG GOr,oR
CElbMlllSTRY
hU3ORATQRY OP 113s RUXcCP lJ OF
3
PIDXWE AND RELATED BASE BY Lours A MIKGSKA. Received September 14, 1920.
The first o€ the cyanine dyes was prepared by WiIliams,l from what we now know t o have been a mixture of lepidine land quinoline, by treatment first with amyl iodide and then with alcoholic potash. The iaiportance of lepidine as a source of cyanine has been considerably diminished by the introduction of pinacyanol, derived from the more easily obtained ouinaldine,2 possessing the same sensitizing properties as cyanine, and obtained in considerably better yield. The recent discovery t h a t from the alkyl halides of lepidiiie and related bases can be obtained, not o~iXgf a nxmber of hitherto unknown dyes of the isocyanine (or pinaverdoll type, but also dyes of a new type,3 possessing interesting and useful senqitizing PI operties in the infra-red, renders the preparation of pure Iepidine in p o d yield again a matter of importance. Several different methods for the preparation of lepidine are quoted in Eeiistein's "Handbook," but without exception they are difficult to carry nut a d disappoirithng in yield and purity of product. T h e fol.10~~1.g procedure has been found to give a fair yield of pure lepidine. of Lepidine.--A mixture of 300 g. of acetone and 300 g of 4 ~ formaldehyde 7 ~ is cooled in ice and saturated with hydrogen chlor ide. After standing overnight a t room temperature, i t is cooled and saturated with hydrogen chloride as ber'ore, and again allowed to stand overnight. It is then slowly added to a cooled mixture of 300 g. of aniline and 600 E;. of hydrochloric acid ( s p ~gr. 1.2). The mixture is heated OD 3 water-bath for 3 hours, under a reflux condenser. Alter cooling it i s neutralized wilh conc. sodium hydroxide solution and extracted with ether The extract is dried over sodium sulfate, the ether distilled off and the residiie distilled. under reduced pressure. To the distillate is added an eqizal weight of acetic anhydride, and the mixture is heated on the steam bath half an hour and then poured into water. The acetanilide and 1x11 changed anhydride are filtered off,and the lepidine recovered by neutral~~~~~~~~~
C Gieville Williams, Chew. Kezds, I , rg (1860) By tieattilent with formaldehyde and -alcoholic alkali, w:th exclusion of air Cf L €3 Wise, E Q Adam, J I< Stewart and C. W Eund, THISJOURNAL, X Y , 4Gc 1
2
(I.319). 8
Kiyptocyanines
E. Q . A d a m and
I, Railer, wilt be published later
iz'ing, extracting and distilling as before. Traces of acetanilide may he removed a t this point by dissolving the lepidine in petroleum ether, filtering, and distilling off the solvent. 'I'he lepidine is dissolved in 1.5 times its own weight of hydrochloric acid (sp. gr. 1 . 2 ) and cooled. A slight excess of sodium nitrite is added and the cold solution extracted wit11 ether (to remo\.e nitroso-tetraliydro-lepidine) . 'Che solution is boiled to decompose the diazo-compound and the phenol formed removed by cxLractiTig the acid solution with ethcr. 'l'lic lepidine is recovered by neutralizing, extracting and distilling as before. I t is then dissolved in an equal weight of 95',:!&alcohol, and Lwice as much alcohol containing a ol sulfuric acid is added. After cooling the sulfate is filtered ofT, n-ashed with cold alcohol and then cthcr. 1:roin the snow-white sullate the lepidine is recovered as I d o r e . 12 yield of 20 g. of lepidine lmiling at 2 6 2 O (at-inosphcricpressure) may be expected. Preparation of p-Tolu-lepidine.---When the aniline is replaced by an equal weight of p-toluidine, the same procedure gives p-tolu-lepidine (i. e., 4,6-dinicthyl-quinoline). Preparation of p-Ethoxy-lepidine.----When the aniline is replaced by ail equa! ncight of p-plienctidinc, the same procedure gives p-ethoxylepidine (i. e., 4-methyl-6-ethoxy-quinoline). 'l'lie product, being solid, may be Lecrystallizcd from petroleum ether. I t then melts a t 77 O. Calc. for CI?N,,P\'O: N , 7 . 4 8 . I'ouiiti: (Kjcldahl) 7.30, 7 . 3 2 , 7 . 3 3 .
,, I lie base gave an ethiodide melting a t I 87 (uncorr.). ,, I h c prvparation of other related bases will be discussed in articles shortly to appear on triinethyl- and tetramethyl-quinolines.
Summary. Rccent clcvclopments in the field of photosensitizing dyes have brought lepidine and related bases again into prominence. A procedure is given for the preparation of lepidine, p-tolu-lepidine and p..cLhoX)'-lepidine. U ' A S ~ ~ ~ N I : I). T UC. N.
