THE ISOXERISM OF THE OXIMES. PART XVI. 547

LXX.-TZie Isomerisl-n of the Oxinzes. Part X V I . Thz Action of Ultra-violet Light on Aldoximes and their Derivatives.

By OSCAR LISLE BRADY and GERALD PATRICK MCHUGH. CIAMICIAN and SILBER (Ber., 1903, 36, 4268) and Dunn and one of us (T., 1913, 103, 1619) showed that 0-, m-, and p-nitroberiz- antialdoximes, when exposed to sunlight in benzer,e solution in glass tubes, are converted into the corresponding syn-isomerides (see also Stoerrner, B e y . , 1911, 44, 667,for the action of ultra-violet light on ketoximes). Ciusa (Atti R. Accad. Lincei, 1906, [v], 15, ii, 72 1) found that p-chloro - and 3-nitro -p -met hoxy- benzantiald- oximes were similarly converted, but was unsuccessful in bringing about isomeric char,ge in the case of benzantialdoxiae a.nd 3 : 4- methylenedioxybenzant~aldoxime ; he inferred therefore that the presence of a negative substituent, such as halogen or the nitro-group, was necessary in the benzene ring for conversion to occur. The object of the present investigation m-as, first, to test the validity of Ciuscz’s claim ; secondly, to ascertain if a more easily controllable source of light could be employed than the sunlight previously used; thirdly, to try whether the action of light would bring about isomeric change in any of the oximes which could not be converted into the syn-isomerides by any of the usual methods ; and, finally, to discover if any derivatives possessing the anti- configuration codd be converted into the corresponding cyn- compounds by the action of light, as in this case no chemical mwns are available, the tendency being for the reverse change to occur.

In aJl, twenty-four aldoximes and derivatives have been sub-

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548 BRADY AND MCHUGH :

mitted to the action of ultra-violet light from a quartz mercury- vapour lamp. It has been found that pmethoxy-, 3 : 4-methyl- enedioxy- benzaniialdoximes and benzantialdoxime are all coii- verted into the syn-isomerides and that Ciusa's supposition does not hold as regards the action of light from this source. The quartz mercury-vapour lamp is a convenient source of light €or bringing about the conversion and, in addition to the three oximes above mentioned, 0-, m-, and p-nitro-, 0-, nz-, and p-chloro-benzanti- aldoximes have been t,ransformed into the corresponding syn- derivatives. The case of o-chlorobenzantialdoxime is of interest, as this compound has not previously been converted into a syn- isomeride, although the latter has been obtained by the action of alkalis on bisnitrosyl-o-chlorobenzyl, (C,H,Cl*CH,),(NO), (Behrend and Nissen, Annalen, 1892, 269, 390). Recently, how- ever, Roper and one of us have succeeded in preparing o-chloro- benzsynaldoxime from the anti-isomeride by a special method (unpublished work).

With two exceptions, all the aldoximes investigated which had previously been obtained in two isomeric forms were almost com- pletely converted into the syn-isomerides. The exceptions were 5-bromo-3 : 4-dimethoxybenzantialdoxime (compare Wentworth and Brady, T., 1920, 117, 10$0), which suffered demethylation, giving 5-bromo-3-methoxy-4-hydroxybenzantialdoxime, and 3 : 4-dimetlz- oxybenzantialdoxime, which underwent no change, although Dunn and one of 11s (T., 1923, 123, 1790) have obtained the syn- isomeride under special conditions.

We have investigated eight aldoximes which cannot be converted into syn-isomerides by any of the usual methods, namely, (1) o-methoxy-, (2) 5-bromo-o-methoxy-, (3) 2 : 4-dinitro-, (4) %nitro- p-dimethylamino-, (5) 6-nitro-3 : 4-methylenedioxy-, (6) 5-nitro- 3 : 4-dimethoxy-, (7) 6-nitro-3 : 4-dimethoxy-, and (8) 5-bromo- 3-methoxy-4-hydroxybenzantinldoximes. In every case, the com- pound when exposed to ultra-violet light underwent no appreciable change. This failure was disappointing, as it was thought that some at least of the oximes which did not form hydrochlorides (Nos, 3, 5, 6, and 7), and therefore could not be transformed in the usual way, would be converted by the action of light.

Eo far, the only derivatives which have been investigated are a number of ethers. The N-methyl ether of benzaldoxime is decom- posed by ultra-violet light with the formation of benzonitrile, whilst the AT-methyl ether of m-nitrobenzaldoxime undergces no change. The 0-methyl ethers of m- and p-nitrobenzantialdoximes are part'ly converted into the corresponding syn-isomerides ; this confirms the results obtained by Dunn and one of us on the action of suiilight

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THE ISOMERISM O F THE OXIMES. PART XVI. 549

on these compounds (T., 1913, 103, 1624). The 0-benzyl ether of p-nitrobenzantialdoxime was converted into the syn-isomeride. This was of some interest, as the 0-benzyl ethers of the syn-oximes had not been previously obtained, but we have now prepared the 0-benzyl ether of p-nitrobenzsynaldoxirne by the action of benzyl chloride on the sodium salt of p-nitrobenzsynaldoxime, when it is formed together with the N-benzyl ether, from which it can be separated by f rac tionatl crystallisation.

One may conclude that, in the case of the aromatic aldoximes, conversion by the action of ultra-violet light is possible only when the two isomerides can be prepared by the usual methods and that the presence of negative groups is not essential as stated by Ciusa- A sufficient number of ethers has not been examined t o enable any conclusion to be drawn, but it appears that the conversion does not take place so readily or so completely as with those oximes which undergo change.

E X P E R I M E N T A L . Oximes .

The general method employed was to dissolve the oxime in a suitable amount of dry benzene and expose it, generally for seventy- two hours continuously, in well-corked, transparent silica tubes to the light from a quartz mercury-vapour lamp. The product was then isolated and its melting point determined; if necessary, it was crystallised from a suitable solvent, care being taken to avoid any risk of isomeric change during the process. If no apparent change had occurred, the product was compared with the original oxime by the method of mixed melting points; if change had occurred, the product was similarly compared with the corresponding syn- isomeride and its configuration determined by the action of acetic anhydride (compare Hantzsch, Ber., 1891, 24, 13). The compound was dissolved in excess of pure acetic anhydride, warmed if iiecessary at 30°, and the solution poured into excess of cold 2N-sodium hydroxide solution. When the exce8s of anhydride was decom- posed, in the case of anti-oximes the acetyl derivative separated, but in the case of syn-oximes the nitrile was formed, as the syn-acetyl compounds are immediately decomposed by cold sodium hydroxide solution. The product was isolated and identified after crystallis- ation by compa'rison with other specimens or hydrolysed, by boiling with sodium hydroxide solution, in the case of the anti-acetyl derivative to the oxime and in the case of the nitrile to the acid, which were identified by comparison with other specimens, the former being precipitated from the alkaline solution with carbon dioxide and the latter by means of hydrochloric acid.

Xyn, m. p. 132").-A solu- Benxantialdoxime (Anti-, m. p. 35".

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550 BRADY AND XCHUGH :

tion of 1 gram of the oxime i n 50 C.C. of dry benzene was divided between five silica tubes. After exposure for seventy-two hours, the solution, although clear, was somewhat brown; it was evapor- ated to small bulk on the water-bath and, after cooling, light petro- leum was added cautiously with stirring and scratching. The precipitated product melted a t 116", and a*fter crystallisation from benzene at 124" J it wzs completely soluble in 2N-sodium hydroxide and was reprecipitated on the addition of ammonium chloride solution. On admixture with benzoic acid, the melting point fell to 78". On determillation of the configuration, an oil having the characteristic odour of benzonitrile m-as obtained which on hydrolysis gave ammonia and benzoic acid.

Xyn, ID. p. 154").- A solution of 1 gram of the oxime in 60 C.C. of dry benzene was divided between six silica tubes. The solution was clear at first, but after exposure for seventy-two hours became brown and a small amount of brown flocculent material separated. The solution mas filtered and light petroleullz added cautiously, when a compouiid melting a t 140-144" was obtained. Crystallisation from benzene e v e a pmduct which was identified as o-nitrobenzsynaldoxime. I n the determination of configuration, o-nitrobenzonitrile was obtained.

111-Nit~ubeizxanti~Zdoxinze (Anti, m. p. 120". Syn, m. p. 123").- One gram of the oxime was dissolved in 60 c.c of hot benzene and the solution cooled rapidly, when part of the oxime separated in a finely divided condition. S ix tubes were used, in three was placed a quantity of the clear supernatant liquor, and in the others the suspension of oxiine in benzene. After seventy-two hours' exposure, all khe tubes contained clear, light brown solutions with a minute amount of brown, eocculent ma,tter a t the bottom. The combined solutions were filtered and the benzene was removed in a current of dry air. The brown residue melted a t 64" and, after crystallisation first from benzene and then from acetone and \va.ter, a product melting at 122" was obtained which was identified as m-nitro- benzsymldoxime. lin. the determination of the configuration m-nitrobenzonitrile and finally m-nitrobenzoic acid were obtained and identified.

p-h7itrobenzantialdox~me (Anti, M. p. 129". Syn, m. p. 184').- The suspension of finely divided oxime obtained by rapidly cooling a solution of 1 gram of the oxime in 30 C.C. of hot benzene was divided between six tubes. After exposure for twenty-four hours, the white, needle-shaped crystals had disappeared and had been replaced by large, brown, rectangular plates adhering to the sides of the tube. These melted at 170" and were identified as p-nitro- benzsynaldoxime. In the determination of the configuration, p-nitrobenzonitrile mas obtained.

o-Nitrobenmntialdozime (Anti, m. p. 102".

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THE ISOMERISX OF TKE OXIMES. PART XVI. 651

0-, m-, and p-Chlorobenxantialdozimes (Anti, m. p.'s 75", 'TO", 106". Syn, m.p.'s 110", 118", 142").--0ne gram of each of the oximes was dissolved in 60 c.c of benzene, in which they were com- pletely soluble in the cold, the solution was divided between six tubes and exposed for seventy-two hours. At the end of that time the solutions were slightly tinged with brown, and in the case of the para-compound crystals had separated on the side of the tube. These melted a t 137-13s" and after crystallisation from benzene at 142". They were identified as p-chlorobenzsynaldoxiine ; the configuration was determined and p-chlorobenzoiiitrile and p-chlorobenzoic acid were obtained. The solutions containing the ortho- a i d meta-compounds were evaporated in a current of dry air, the product in each case mas pressed on porous tile and washed with a little benzene, when white crystals melting at 98-100" and 114") respectively, were obtained. Crystallisation from benzene raised these to 110" and 118", and the compounds x-ere idezitified as o-chlorobenzsynaldoxime and m-chlorobenzsynaldoxirne. In the determination of the configuration, 0- and m-chlorobeiizonitriles and 0- and m-chlorobenzoic acids were isolated.

p-~lethox~benxanticr2doxinie (Anti, m. p. 61". S p , m. p. 132').- One gram of the oxime mas dissolved in 10 C.C. of benzene in the cold and exposed in one tube for seventy-two hours. At the end of that time, rectangular plates had separated on the sides of the tube; these melted a t 127" and after crystallisation from benzene at 130". The prcduct was identified as p-methoxybenzsynaldoxime and in the determination of the configuration p-methoxybenzoic acid was obtained.

3 : 4-Il~ethylenedioxyberzxantiak~oxime (Anti, rn. p. 110". S$n, m. p. l4Go).--One gram of the oxime was dissolved in 60 C.C. of cold benzene, the solution divided between six tubes acd exposed for seventy-two hours. The solution turned brown and z small amount of flocculent material was precipitated ; it was filtered and the oxime precipitated by the cautious addition of light petroleum. The precipitate melted a t 134-136" and after crystallisation from benzene at 143". It was identified as 3 : 4methylenedioxybenzsynaldorrime ar,d in the determination of the configuration 3 : 4-methylemdioxy- benzonitrile and the correspoding acid were obtaired.

Syz, m. p. 116").-04 Gram of the oxime was suspended in 40 C.C. of benzene divided between four tubes. After exposure for seventy- two hours, when the suspension had turned brown, the solid was collected and found to melt a t 176" and after crystallisation from benzene a t 179". The prcduct was identified as 5-bromo-3-methoxy- 4-hydroxybepzantialdoxime by comparison with another specimen of that compound.

5-Bromo-3 : 4-dimethoxybeneantialdoxime (Anti, m. p. 83".

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552 BRADY AND MCHUGH :

o-3!Iethoxy-, 3 : 4-Dimethoxy-, 2 : 4-Dinitro-, 3-Nitro-p-dimethyl- amino- , 6- Nitro- 3 : 4-meth ylenediox y-, 5 - Bromo- o -ntethoxy - , 6- Nitro - 3 ; ct-dimethoxy-, 5-Nitro-3 ; 4-dimethoxy-, and 5-Bromo-3-methoxy-4- hydroxy-benxantia1doximes.-From 2.0 grams to 0.5 gram of the respective oximes were dissolved in 50 c.c of benzene, according t o solubility, and exposed in six tubes for seventy-two hours. In no case was there any evidence of conversion into the syn-isomeride, for in every instance the original oxime was recovered unchanged and characterised by comparison with another specimen. In addi- tion, the crude product was fractionally crystallised, but no indication was obtained of t'he presence of the syn-isonieride.

Ethers. 0-Methyl Ether of m-Nitrobenzantialdoxime (Anti, m. p. 63".

Syn, m. p. 74").-Three grams of the ether (m. p. 63") were dissolved in 30 C.C. of benzene, the solution divided between six tubes, and exposed for 45 hours. The crude product obtained by evaporating the benzene melted at 4 0 4 5 " ; this was dissolved in warm alcohol and the solution fractionally precipitated by the addition of water with thorough stirring and scratching. Six crystalline fractions were obtained. The first two, melting at 54-56" and 55-57', showed a rise of melting point when they were mixed with an equal amount of the original ether ; the melting points of the remaining four fractions were lowered by admixture. Fractions 5 and 6 were recrystallised from alcohol and the first crystals separating were again crystallised from alcohol, when a product melting a t 66-68" was obtaiiied which on admixture with the 0-methyl ether of ~n-nihrobeazs~naldoxi~e (m. p. 74") melted a't 68-72'. The solvent was then changed, and the second crop of crystals from t'he crystallisation of fractions 5 and 6 crystallised from light petroleum, when a product melting a t 71-73" was obtained. Fractions 4 and 5 were then crystallised twice from light petroleum, when a product melting at 73-74" was obtained which did not depress the melting point of the syn-ether.

0-illethyl Ether of p-Nitrobe?zxantialdozime (Anti, m. p. 104". Xyn, in. p. 70°).--The evidence obtained in this case was not so conclusive as with the meta-compound. Unfortunately, the syn- ether melts at a lower temperature than the anti-ether, and addition of the anti-ether t o it raises the melting point. When, however, 0-7 gram of the 0-methyl ether of p-nitrobenzantialdoxime (m. p. 101') in 50 C.C. of benzene in five tubes was exposed for seventy- two hours and the solution evaporated, the product melted at 80-84". Practional crystallisation from alcohol and recrystallis- ation of the more soluble portion gave a product melting at 72--73", which was not changed on further crystallisation. Adrnishure with

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THE ISOMERISM O F THE OXIMES. PART XVI. 553

the 0-methyl ether of p-nitrobenzsynaldoxime (m. p. 70") did not change this, so that it is unlikely that it was a decomposition pro- duct of some kind.

0-Benxyl Ether of p-Nitrobenxantialdoxime (Anti, m, p. 118". Xyn, m. p. 64").-One gram of the ether (m. p. 118") in 50 C.C. of benzene was divided between five tubes and exposed for seventy- two hours. The benzene was removed on the water-bath and the product, which melted over a range of 64" t o go", was crystallised from alcohol, when the crystals which separated mere found to be the original ether. The mother-liquor was cautiously diluted with water; the first crop of crystals obtained was again the original ether, but the next five crops all melted very close to 64". These were combined and cryatallised from light petroleum, when the 0-benzyl ether of p-nitrobenzsynaldoxime was obtained as a pale yel- low, crystalline powder, m. p. 64" (Found : N = 11.1. C,,H1,03N2 requires N = 10.9 per cent.). The compound was found to be identical with the 0-benzyl ether prepared from p-nitrobenzsyn- aldoxime in a way analogous to the preparation of the syn-0-methyl ethers. *

N-1Methyl Ether of Benxaldoxime.-One gram of the ether in 50 c.c. of benzene divided between five tubes was exposed for seventy-two hours. The solution, which had turned brown and deposited a trace of sediment, was filtered and on evaporation yielded an uncrystallisable oil with a strong odour of benzonitrile. This on hydrolysis yielded benzoic acid and ammonia. In another experi- ment, in which the exposure was for twenty-four hours, benzonitrile and a small amount of unchanged N-ether were obtained.

N-Methyl Ether of m-Nitrobenxa1doxime.-One gram of the ether dissolved in ti0 C.C. of benzene in five tubes was exposed for seventy- two hours. A few greenish-yellow crystals separated from the solution, and these proved to be the unchanged ether. The solution on evaporation gave a product melting a t 94-106", but on crystal- lisation only unchanged N-methyl ether could be isolated. The lowering of melting point indicates some change, but it is apparently very small.

* Three grams of p-nitrobenzsymldoxime were dissolved in alcohol and treated with 0.4 gram of sodium, dissolved in alcohol, and 1.7 grams of benzyl chloride. The mixture was boiled under reflux for an hour and diluted with water, when a yellow solid was obtained; this was separated, washed with sodium hydroxide solution to remove unchanged oxime, and then with water. The bulk of the product, aa would be expected, consisted of the N-benzyl ether, which is less soluble than the 0-benzyl ether. By a long series of fractional crystallisations from alcohol, ether, and light petroleum, a small quantity of the 0-ether was obtained, nielting a t 64", which did not, on admixture, depress the melting point of the compound obtained a hove.

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554 DEY AND ROW :

In conclusion, the authors wish to express their thanks to the Government Grant Committee of the Royal Society for a grant which has, in part, defrayed the expenses of this work.

THE RALPH FORSTER LL4BORATORY O F ORGAFIC CHEMISTRT,

UNIVERSITY COLLEGE, LONDON. [Received, Decembcr 13th, 1933.1

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