Oximes caution

Dissolve 5 g. of hydroxylamine hydrochloride in 10 ml. of water in a small conical flask and add a solution of 3 g. of sodium hydroxide in 10 ml. of water. Cool the solution in cold or ice water, and add 6 g. (7-6 ml.) of acetone slowly. Cool the flask, shake well, and leave overnight, during which time the oxime may crystallise out. If no crystals appear, cork the flask and shake vigorously when the acetoxime usually separates as colourless crystals. Filter the crystals at the pump, dry rapidly between filter paper (yield 2- 6 g.) and determine the m.p. (59°). Extract the filtrate with two 20 ml. portions of ether, and remove the solvent a further 0 - 5 g. of acetoxime (m.p. 60°) is obtained. Recrystallise from light petroleum, b.p. 40-60° CAUTION inflammable) to obtain the pure acetoxime, m.p. 60°. Acetoxime sublimes when left exposed to the air. 

Beckmann rearrangement of benzophenone oxime to benz-anilide. Dissolve 2 g. of benzophenone oxime in 20 ml. of anhydrous ether in a small conical flask and add 3 g. of powdered phosphorus pentachloride (or 3 ml. of pure tbionyl chloride). Distil off the solvent and other volatile products on a water bath CAUTION ether), add 25 ml. of water, boil for several minutes and break up any lumps which may be formed. Decant the supernatant liquid, and recrystallise, in the same vessel, from boiling alcohol. The product is benzanilide, m.p. 163° confirm this by a mixed m.p. determination with an authentic specimen. 

Both base and noble-metal catalysts have been used with success in the hydrogenation of oximes. Base metals, such as nickel 1,13,50,76) or cobalt 26,63), are used at elevated temp>eratures and pressures ( 80-l00 "C, 100 atm), and under these conditions runaway reactions have occurred with easily reduced compounds. Due caution must be exercised by limiting the catalyst or hydrogen or by sufficient dilution with solvent 22). 

Reaction with alcohols is general for diazo compounds, but it is most often performed with diazomethane to produce methyl ethers or with diazo ketones to produce a-keto ethers, since these kinds of diazo compounds are most readily available. With diazomethane593 the method is expensive and requires great caution. It is used chiefly to methylate alcohols and phenols that are expensive or available in small amounts, since the conditions are mild and high yields are obtained. Hydroxy compounds react better as their acidity increases ordinary alcohols do not react at all unless a catalyst such as HBF4594 or silica gel595 is present. The more acidic phenols react very well in the absence of a catalyst. Oximes, and ketones that... 

In an alternate procedure, the last step is carried out in acetonitrile using the same quantities. During the addition of the diamine, the solution is maintained at 5°C, allowed to rise slowly to room temperature for about 15 min, and then warmed to about 75°C for one-half hour. ( Caution. The temperature must be monitored closely since the reaction is strongly exothermic.) The relatively pure amine oxime hydrochloride (PnAO 2HC1) is collected on a filter and washed with 50-mL portions of acetonitrile and dried in air. 

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.)... 

It has been almost 40 years since B. Wilson et al. observed that nucleophiles, oximes like hydroxamic acid, reactivated OP-inhibited AChE above and beyond that occurring from spontaneous reactivation, opening the way to a treatment for OP poisoning. The oxime registered for use in the United States is 2-PAM Cl (Protopam) its methanesulfonate salt (P2S) is used in Europe. Oxime therapy should be recommended with caution for carbamate poisonings. Although beneficial in the case of aldicarb, there is evidence that 2-PAM treatment increases the toxicity of carbaryl. 

Fluorination. In a freon solvent, this powerful fluorinating agent is able to convert compounds containing C=N (ketone oxime ethers, hydrazones) and C=S groups to gew-difluorides. Trifluoromethyl derivatives are directly obtained from alkyl dithioates. Caution must be paid to avoid the use of oxygenated solvents with which BrFi reacts violently. 

Caution Heating neat lEM-blocked with oximes at or about lOO C may produce an exotherm which may initiate... 

Hydroxylamine is known to be highly toxic to plants so the possibility that it is an obligatory intermediate in nitrate reduction must be considered with caution. Interest in hydroxylamine arises from the lengthy controversy, briefly mentioned here, concerning the rela-j five merits of hydroxylamine or ammonia as the key intermediate in nitrogen fixation. The toxicity of hydroxylamine may well be due to its action as an enzyme inhibitor. However, in spite of its toxicity, there are still some claims that hydroxylamine may be an intermediate in the formation of amino acids by oxime formation with such carbonyl compounds as glyoxilic acid (formed in photosynthesis), I pyruvate, a-ketoglutarate or oxaloacetate (intermediates in carbo-... 

---