Acetoxime

The bleaching powder acts as though it consisted of a compound of calcium hydrate and chlorine, and the process probably occurs in two stages. 

Trichloracetone is first formed, which is then decomposed by 

Properties.—Colourless liquid possessing a sweet smell, b. p. 60—62° sp.gr. 1-498 at 15° very slightly soluble in water non-inflammable. As chloroform slowly decomposes in presence of air and sunlight into phosgene, it is usual to add a little alcohol to the commcicial product, which arrests the change. Pure chloroform is neutral to litmus, has no action on silver nitrate solution and does not discolour concentrated sulphuric acid when shaken with it for an hour or left for a day. 

Reactions.—i. Heat a few drops with double its volume of methyl alcoholic potash. On the addition of water a clear solution is obtained. Potassium formate and chloride are formed. CPICl3 + 4KOH = 3KC1+HC0.0K + 2H,0. 

Bring into a test-tube two drops of chloroform, one drop of aniline and i c.c. of alcoholic potash and warm zw the fume cupboard. Note the intolerable smell of phenyl carbamine (carbamine reaction), CHClj-bCQH3NHo-b3KOH=CQH5NC + 3KCI-t-3H.2O. Wash out the contents of the test-tube in the fume cupboaid. 

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The oxime is freely soluble in water and in most organic liquids. Recrystallise the crude dry product from a minimum of 60-80 petrol or (less suitably) cyclohexane for this purpose first determine approximately, by means of a small-scale test-tube experiment, the minimum proportion of the hot solvent required to dissolve the oxime from about 0-5 g. of the crude material. Then place the bulk of the crude product in a small (100 ml.) round-bottomed or conical flask fitted with a reflux water-condenser, add the required amount of the solvent and boil the mixture on a water-bath. Then turn out the gas, and quickly filter the hot mixture through a fluted filter-paper into a conical flask the sodium chloride remains on the filter, whilst the filtrate on cooling in ice-water deposits the acetoxime as colourless crystals. These, when filtered anddried (either by pressing between drying-paper or by placing in an atmospheric desiccator) have m.p. 60 . Acetoxime sublimes rather readily when exposed to the air, and rapidly when warmed or when placed in a vacuum. Hence the necessity for an atmospheric desiccator for drying purposes. 

Hydrolysis of Acetoxime. Place about i g. of the recrystallised oxime in a small distilling-flask (50 ml.), add 10 ml. of dilute HjSO, and heat gently until about half the solution has distilled over. Test [a] the aqueous distillate for acetone by the iodoform reaction (p.346), b) the residual solution in the distilling-flask for hydroxylamine by... 

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. 

In turn, a lipase-promoted acylahon of prochiral substrates 104, using lipases from Candida cylinracea and Chromobacterium viscosum and methyl isobutyrate or acetoxime isobutyrate as the acyl donors, gave the product 105 in yields up to 80% and with ees up to 75% (Equahon 50). ... 

Hydrolysis of oximes catalyzed by transition-metal complexes has not been studied prior to a report by Kostic et al. They have reported kinetics of hydrolysis of acetoxime to acetone catalyzed by two palladium(II) complexes, identified active species in the hydrolysis reaction, proposed a reaction mechanism, and fully characterized a bis(acetoxime) complex that is relatively stable toward hydrolysis.458... 

The constituent of paint, 2-nitropropane, exhibiting genotoxicity and hepatocarcinogeni-city was oxidized by liver microsomes forming nitric oxide, which was identified as a ferrous NO complex [61]. Clement et al. [62] concluded that superoxide may participate in the microsomal oxidation of /Y-hydroxyguanidincs, which produced nitric oxide, urea, and the cyanamide derivative. Caro et al. [63] suggested that the oxidation of ketoxime acetoxime to nitric oxide by microsomes enriched with P-450 isoforms might be mediated by hydroxyl or hydroxyl-like radicals. 

Pt(a-alaninate)(H20)L] (L = NH3, py, Et2S, or DMSO) has shown that the acidity varies greatly with the nature of the cis-L. As expected, the 7r-donor NH3 causes the weakest acidic properties, whereas 7t-accepting ligands produce a marked increase in for the water. Similar studies on trans-[Pt(DMSO)-C1L(H20)] indicate that the acid strengths decrease in the order L = NH2OH > acetoxime > acetaldoxime. ... 

Structurally similar seven-membered dihydro-l,2,7-thiadiazepine 69 and l,2,7-thiadiazepan-3,6-dione 70 were obtained by an unexpected dimerization of acetoxime 71 (1997BSB605) and a ring closure of dicarboxamide 72 (1995CC1449). Curiously, the reaction of sulfur monochloride containing two sulfur atoms in both cases led to the insertion of one sulfur atom to the seven-membered ling or three sulfur atoms to the by-product 73 in the second reaction, but not two sulfurs (Scheme 36). 

We shall now compare some properties of prototypical examples of hydroxylamines, oximes and hydroxamic acids. These will be structures 1, 2 and 3 with methyl groups at the remaining positions, i.e. dimethylhydroxylamine (6), acetoxime (7) and acetohydroxamic acid (8). 

TABLE 3. Some computed properties of dimethylhydroxylamine (6), acetoxime (7) and acetohy-droxamic add (8) ... 

As is the case for acetoxime, 7, the two isomers of this oxime are both planar (except for two methyl hydrogens in each case). Their energy difference, E anti)—E(syn), is only 0.7 kcalmoH (Table 4), while AG actually has the opposite sign, but is also very small. At the B3LYP/6-31 lG(3df,2p) computational level, we can only conclude that these two isomers are intrinsically very similar in stability. If one or the other is found to be... 

As points of reference, we will take two well-established hydrogen-bond donor/ acceptors, H2O and NH3. Their computed gas-phase Vs,max and Vs,mm are in Table 5, along with the same data for all of the molecules that have been discussed hydroxylamine (5), dimethylhydroxylamine (6), acetoxime (7), acetohydroxamic acid (8), and the isomeric pairs of oximes examined in the last section. Finally, we included an additional hydroxamic acid, 11, to see the effects of the strongly electron-withdrawing cyano group. 

The /s.min of 12.9 eV of neutral acetoxime implies that it should also act as a base, somewhat weaker than pyridine. Indeed an important application, especially of the double oxime dimethylglyoxime (12), is in chelating metal ions. ... 

Figure 4 provides an interesting contrast to Figure 3. The latter shows very clearly the nitrogen and oxygen lone pairs in acetoxime, (H3C)2C=N—OH. However, Figure 4 indicates that the most polarizable region is not one of these lone pairs, but rather above and below the C=N double bond. This is followed in polarizability by the nitrogen lone pair, its sp form being very apparent.

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