A-Oximation

Usually prepared by the action of NaCN on benzaldehyde in dilute alcohol. It is oxidized by nitric acid to benzil, and reduced by sodium amalgam to hydrobenzoin PhCHOHCHOHPh by tin amalgam and hydrochloric acid to des-oxybenzoin, PhCH2COPh and by zinc amalgam to stilbene PhCH = CHPh. It gives an oxime, phenylhydrazone and ethanoyl derivative. The a-oxime is used under the name cupron for the estimation of copper and molybdenum. 

D. Benzoin-a-oxime (cupron) (VII). This compound yields a green predpitate, CuC14Hu02N, with copper in dilute ammoniacal solution, which may be dried to constant weight at 100 °C. Ions which are predpitated by aqueous ammonia are kept in solution by the addition of tartrate the reagent is then spedfic for copper. Copper may thus be separated from cadmium, lead, nickel, cobalt, zinc, aluminium, and small amounts of iron. 

From strongly addic solutions benzoin-a-oxime precipitates molybdate and tungstate ions quantitatively chromate, vanadate, niobate, tantalate, and palladium) II) are partially predpitated. The molybdate complex is best ignited at 500-525 °C to Mo03 before weighing alternatively, the predpitate may be dissolved in ammonia solution and the molybdenum predpitated as lead molybdate, in which form it is conveniently weighed. 

Benzoin-a-oxime is a white, crystalline solid, m.p. 152 °C, which is sparingly soluble in water but fairly soluble in ethanol. The reagent is employed as a 2 per cent solution in ethanol. 

Benzoin-a-oxime (cupron). Copper(II) ( > 50mg in ammoniacal solution). Add 2 per cent ethanolic solution of the reagent to the boiling solution, filter and wash the precipitate with hot dilute ammonia solution (1 100), then with hot water and finally with warm ethanol. Dry at 105-115 °C and weigh as Cu(C,4H,, 02N) (Section 11.26). 

In a very interesting paper, Rtiedi and colleagues have presented a convenient a-oximation method that allows for the selective preparation of 1,2-dione monoximes 38a, 40a, 41a and/or their hydrolyzed 1,2-diketone derivatives 38b, 40b, 41b simply by using the appropriate amount of the in situ generated nitrosyl chloride and ketones 37 or 39 (Scheme 26 route a or b). 

The novel X-ray crystal structures of the following have all been reported 5-amino-4-(4-methoxyphenyl)-2-phenyl-7-(pyrrolidin-l-yl)-[l,6]naphthyridine-8-carbonitrile <1999AXC1670>, 5-amino-4-(4-diethylaminophenyl)-2-(4-hydroxy-phenyl)-7-(pyrrolidin-l -yl) [ 1,6]naphthyridine-8-carbonitrile <2001 AXC726>, 5-amino-4-(4-diethylaminophenyl)-2-phenyl-7-(pyrrolidin-l-yl)[l,6]naphthyridine-8-carbonitrile <2000AXC80>, and rotenone a-oxime <2003AXC392>. 

Benzilmonoxime. Boil 10 g. of the pure a-monoxime for 15 minutes with 1 g. of dried animal charcoal in a quantity of pure benzene just sufficient to dissolve the a-monoxime at the boiling point. Filter off the charcoal and allow the filtrate to stand. The p-monoxime + 0-5 C6Hg crystallises slowly on cooling a further crop can be obtained by evapora tion of the mother liquid. An excellent yield of the p-monoxime, m.p. 112°, is obtained. The pure 8-oxime causes no colour change with aqueous - alcoholic copper acetate solution if it is contaminated with the a-oxime, a greenish colour is produced. 

Fig-1, (a) oxime conversion, (+ ) ceprolactam selectivity and ( ) caprolactam yield with time using 0.1 g boria on alumina catalyst at a reaction temperature of 300 C. 

Fig.4. (a) Oxime conversion, (b) Caproiactam selectivity, (c) Caproiactam Yield using 0.2g (.) boria on alumina, M regenerated boria on alumina and (+) alumina catalyst at 300 C for 30 hours. 

P-Benzilmoitoxime. The a-oxime is converted into the /J-form by treatment with a solution of hydrogen chloride in benzene (CAUTION) (or ether) at room temperature. From benzene, solvated crystals which melt on rapid heating at about 65 °C are obtained. Removal of benzene of crystallisation in an oven at 50 °C and recrystallisation from carbon disulphide (CAUTION) yields pure /J-benzilmonoxime, m.p. 112°C. The product gives no colour change with aqueous-alcoholic copper acetate solution if it is contaminated with the a-form a greenish colour is produced. (Conversion of the a-form into the / -form may also be effected by boiling in benzene solution in the presence of animal charcoal, which presumably contains adsorbed acidic catalysts.)... 

Chiral 1,2-oxazines (33) have been prepared from achiral ketones, R -CO-CfT-R2, via an a-oximation step (with a tetrazolylpyrrolidine organocatalyst), followed by a Wittig reaction.87 Subsequent N—O cleavage yields enantiopure ds-allylic alcohols bearing a pendant amine. 

Oximes Cupric chloride (0.5%) Immediate green spots (p-oximes) green-brown spots after 10 min (a-oximes) 74... 

Reaction of benzoin-a-oxime with sodium hydride in propan-2-ol produces 1,5-dianion which is further cyclized into 1,5,6-dioxazocine ring system with 1,3-dibromopropane (Equation 29 <2004S837>). 

The configuration of the oxime is important to the course of the reaction. Thus, while the j8-oxime (11) gives the indoxazene or its degradation products, the a-oxime (12) undergoes a Beckmann rearrangement, finally yielding benzoxazole (13). This difference in reaction pathway between stereoisomeric oximes was used in the determination of their configurations.7,8 22,23... 

All of these complexes decompose cleanly at low temperature to produce acetonitrile, carbon dioxide, and initially, the metal hydroxide (equation 45). The decomposition temperatures are 144,176, and 198 °C for Ba, Cu, and Y, respectively. In the case of copper and yttrium, the final product is the metal oxide produced by the dehydration of the hydroxide, while barium hydroxide recombines with carbon dioxide to yield the carbonate. Barium carbonate formation can be avoided, however, by use of a different ligand that avoids carbon dioxide formation. Benzoin a-oxime (Hbo) (13) has been found to be a quite suitable diprotic ligand for this purpose. The barium salt is easily prepared by reaction of the oxime with the metal dihydride (equation 46), and it decomposes cleanly to barium oxide by loss of benzaldehyde and benzonitrile at 250 °C (equation 47). 

Intramolecular participation of a neighboring hydroxy group is observed in the rearrangement of erythromycin A oxime (24) with p-toluenesulfonyl chloride and sodium hydrogencarbonate in acetone-water (equation 12). Interestingly, with the same reagent in pyridine-ether only the normal rearrangement product (25) is formed. 

It is pseudoisatinethyl-a-oxime. On further ethylation the diethyl ether is formed ... 

The diethyl ether of pseudoisatin-a-oxime yields diethyl indigo blue if treated with mild reducing-agents, precisely in the same manner that pseudoisatoxime gives indigo blue under similar conditions. 

---