The product mixture labeled A was chromatographed on a silica gel column (200 g) by elution with hexane-diisopropyl ether (4:1). First fractions gave 3b (0.51 g): mp 170 °C (from re-hexanechloroform);

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T h e chain-terminati~~g step in the photochemical oxidation of acetaldehyde in the gas phase has earlier been established to be the reaction 2 A c 0 0 = AcOOAc + 0 2 .Using 0x5 gen-18 of 99.4y0 purity in the form of molecular oxygen we have made a careful study of the variation of the isotopic ratios of the various oxygens, by mass spectrometry, during the course of the photooxidation. The results show conclusively that the mechanism of the termination step is:AcOO + AcOW* = AcOO*Ac + OO*, where 0" represents 018. Thus the recombination terminating reaction takes place with the elimination of one oxygen atom from each reacting peroxy XcOO radical. The mechanism of this elimination process is thought to be as folloms: ISTRODUCTIOKThe thermal and photochenlical oxidations of acetaldehq-de in the gas phase both lead to the main product peracetic acid. I t has also been established (1-4) that the terminatingstep in these oxidation reactioils is the recombination of chain carrier and that the radical involved is the peroxyacetyl radical CHaCO3. In the case of the low temperature phase photooxidation of acetaldehyde the following kinetic inecllanisin (2-4) has been found to be in agreement with the experimental data for the processes leading to peroxide CH3 + 0 2 1 = R CHO + 0 2 1

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Reaction of acetoacetic esters (3) with acetyl nitrate (1) at -10 to 15°in the presence of catalytic amounts of strong protic acids or Lewis acids afforded 90-97% yields of the corresponding nitroacetoacetic esters (6). Linder similar conditions, ethyl 3-acetoxy-2-butenoate (10b) produced 63% 6b and 35% 3,4-bis(ethoxycarbonyl)furazan 2-oxide (9b) at 15°. In the absence of catalyst, reaction of ethyl acetoacetate (3b) was slow at 25°and the yields of 6b and 9b were 39 and 52%, respectively. A slow transformation of 6b to 9b took place at 22°in the presence of catalytic amounts of H2SO4 and the reaction was accelerated by acetic anhydride. Proton exchange evidence indicated that the crucial function of the acid catalyst in the nitration is to protonate 1 to provide an active nitrating species 2, rather than merely accelerate enolization of 3. In the presence of water, alcohols, or ammonia 6 cleaved quantitatively to nitroacetate esters and correspondingly acetic acid, acetate ester, or acetamide. The cleavage With water and alcohols was acid catalyzed. The combination of nitration and cleavage reactions affords a practical synthesis of nitroacetate esters.