Reactions 1,1-diacylation

The product of this reaction is an imide (Section 20 16) a diacyl derivative of an amine Either aqueous acid or aqueous base can be used to hydrolyze its two amide bonds and liberate the desired primary amine A more effective method of cleaving the two amide bonds is by acyl transfer to hydrazine... 

Carboxylic acid hydiazides are prepared from aqueous hydrazine and tfie carboxylic acid, ester, amide, anhydride, or halide. The reaction usually goes poody with the free acid. Esters are generally satisfactory. Acyl halides are particularly reactive, even at room temperature, and form the diacyl derivatives (22), which easily undergo thermal dehydration to 1,3,4-oxadiazoles (23). Diesters give dihydtazides (24) and polyesters such as polyacrylates yield a polyhydrazide (25). The chemistry of carboxyhc hydrazides has been reviewed (83,84). 

Diacyl peroxides are used in a broad spectmm of apphcations, including curing of unsaturated polyester resin compositions, cross-linking of elastomers, production of poly(vinyl chloride), polystyrene, and polyacrjlates, and in many nonpolymeric addition reactions. 

Aromatic diacyl peroxides such as dibenzoyl peroxide (BPO) [94-36-0] may be used with promoters to lower the usehil decomposition temperatures of the peroxides, although usually with some sacrifice to radical generation efficiency. The most widely used promoter is dimethylaniline (DMA). The BPO—DMA combination is used for hardening (curing) of unsaturated polyester resin compositions, eg, body putty in auto repair kits. Here, the aromatic amine promoter attacks the BPO to initially form W-benzoyloxydimethylanilinium benzoate (ion pair) which subsequentiy decomposes at room temperature to form a benzoate ion, a dimethylaniline radical cation, and a benzoyloxy radical that, in turn, initiates the curing reaction (33) ... 

Petoxycatboxyhc acids also have been prepared by the reaction of acid chlorides, anhydrides, or boric-catboxyhc anhydrides with hydrogen or sodium peroxide. These reactions ate carried out at low temperature and with excess peroxide to avoid the formation of diacyl peroxides (44,168,181,184). 

This ladical-geneiating reaction has been used in synthetic apphcations, eg, aioyloxylation of olefins and aromatics, oxidation of alcohols to aldehydes, etc (52,187). Only alkyl radicals, R-, are produced from aliphatic diacyl peroxides, since decarboxylation occurs during or very shortiy after oxygen—oxygen bond scission in the transition state (187,188,199). For example, diacetyl peroxide is well known as a source of methyl radicals (206). 

The fate of the ion pair iatermediate depends on the stmcture of the amine and the reaction conditions. Certain tertiary amines, eg, dimethylaruline (DMA), react with specific diacyl peroxides such as diben2oyl peroxide (BPO) to generate free radicals at ca 20°C. Some reactions, eg, DMA—BPO, are explosive when neat reactants are mixed. Primary and secondary amines do not yield free radicals. 

Nonhindered phenols are acyloxylated by diacyl peroxides ia nonradical reactions (187) ... 

Phenols with bulky ortho- and para-substituents, eg, phenoHc antioxidants, do not undergo this reaction however, they scavenge radicals generated by thermolysis of diacyl peroxides and other peroxides. Diacyl peroxides react with potassium superoxide, KO2, forming singlet oxygen (207). 

Synthesis. Symmetrical diacyl peroxides (20, R = R = alkyl or aryl) are prepared by the reaction of an acyl chloride or anhydride with sodium peroxide or hydrogen peroxide and a base ... 

Use of diacid chlorides for acyl chlorides in the latter reaction results in generation of di(diacyl peroxides) (25). 

Other unsymmetrical peroxides can be prepared by this reaction by employing other acylating agents, eg, alkyl chloroformates, organosulfonyl chlorides, and carbamoyl chlorides (210). Unsymmetrical and symmetrical di(diacyl peroxides) also are obtained by the reaction of dibasic acid chlorides directiy with peroxycarboxyhc acids or monoacid chlorides directiy with diperoxycarboxyhc acids in the presence of a base (44,187,203). 

Polymeric diacyl peroxides (26) can be prepared from the reaction of dibasic acid chlorides, eg, succinoyl, fumaryl, sebacoyl, and terephthaloyl chlorides, with sodium or hydrogen peroxide (187). 

Acylation. Reaction conditions employed to acylate an aminophenol (using acetic anhydride in alkaU or pyridine, acetyl chloride and pyridine in toluene, or ketene in ethanol) usually lead to involvement of the amino function. If an excess of reagent is used, however, especially with 2-aminophenol, 0,A/-diacylated products are formed. Aminophenol carboxylates (0-acylated aminophenols) normally are prepared by the reduction of the corresponding nitrophenyl carboxylates, which is of particular importance with the 4-aminophenol derivatives. A migration of the acyl group from the O to the N position is known to occur for some 2- and 4-aminophenol acylated products. Whereas ethyl 4-aminophenyl carbonate is relatively stable in dilute acid, the 2-derivative has been shown to rearrange slowly to give ethyl 2-hydroxyphenyl carbamate [35580-89-3] (26). 

Reactions of quinones with radicals have been explored, and alkylation with diacyl peroxides constitutes an important synthetic tool (68). Although there are limitations, an impressive range of substituents can be introduced in good yield. Examples include alkyl chains ending with functional groups, eg, 50% yield of (70) [80632-67-3] (69,70). 

The NOBS system undergoes an additional reaction that forms a diacyl peroxide as a result of the nucleophilic attack of the peracid anion on the NOBS precursor as shown in equation 21. This undesirable side reaction can be minimized by the use of an excess molar quantity of hydrogen peroxide (91,96) or by the use of shorter dialkyl chain acid derivatives. However, the use of these acid derivatives also appears to result in less efficient bleaching. The dependence of the acid group on the side product formation is apparentiy the result of the proximity of the newly formed peracid to unreacted NOBS in the micellar environment (91). A variety of other peracid precursor stmctures can be found (97—118). 

Isoxazole, 3-chloro-5-hydroxymethyl-oxidation, 6, 27 Isoxazole, 4-chloromethyI-reactions, 6, 53 Isoxazole, 5-chloro-3-phenyl-reactions, 6, 58 Isoxazole, 3-cyano-reactions, 6, 30 Isoxazole, diacyl-synthesis, 6, 79 Isoxazole, 3,4-dialkyl-synthesis, 6, 83 Isoxazole, 3,5-dialkyl-synthesis, 6, 83 Isoxazole, 4,5-dialkyl-synthesis, 6, 83 Isoxazole, 3,5-diamino-2-amino-l-azirines from, 7, 89 Isoxazole, 3,5-diaryl-synthesis, 6, 63 Isoxazole, 2,5-dihydro-synthesis, 6, 79 Isoxazole, 4,5-dihydro-dehydrogenation, 6, 4... 

The reactions of copper salts with diacyl peroxides have been investigated quite thoroughly, and the mechanistic studies indicate that both radicals and carbocations are involved as intermediates. The radicals are oxidized to carbocations by Cu(II), and the final products can be recognized as having arisen from carbocations because characteristic patterns of substitution, elimination, and rearrangement can be discerned " ... 

The procedure which had originally been used by Lehn et al. involved slow addition (over a period of ca. 8 h) of ca. 0.1 M solutions of diamine and diacyl halide in benzene. Dye et al. found that the reactions could be conducted more rapidly as long as stirring was kept efficient. This observation suggested the use of a mixing chamber of the type normally used for stopped-flow kinetic studies. Utilizing this type of set-up, the latter authors were able to obtain a 70% yield for 1, slightly inferior to the yield reported by Lehn, but a similar yield of 3 which is better than that previously ob-tained. Note that the chemical features of this synthetic method are essentially identical to the approach shown in Eq. (8.1) and differ primarily in the mechanics. 

Lehn and his coworkers have prepared a number of chiral cryptands based upon the 2,2 -binaphthyl unit " . In a typical preparation, the binaphthyl units are treated with bromoacetic acid to form the phenoxyacetic acid derivatives which are then converted into the corresponding diacyl chlorides (75). Reaction of 15 with l,10-diaza-18-... 

Alk = Et), a-methylstyrene (156, Ar = Ph), and allyl-benzene (160, Ar = Ph) are representatives of the four types of monosubstituted propenes (olefins 157 and 158, etc. written in Table I as equilibrium pairs undergo equilibration during the course of the reaction and yield the same pyrylium salt on diacylation). Disubstituted propenes which gave pyrylium salts on diacylation are 2-pentene (163, Alk = Me) and 1,2-diphenylpropene (164, Ar = ph),305 3-ethyl-2-pentene represents a trisubstituted propene... 

An unusual dependence of the structure of the reaction product on the acylating agent (catalyst and acyl group) was observed by Balaban and Nenitzeseu in the diacylation of olefins 195, where R = Me (2-methyl-2-butene ) or R = Ph (2-methylpropenyl-benzene ) strong catalysts like AlClg or SbCls promote the formation of the 2,4,6-trisubstituted compound 197, whereas weaker... 

Goldschmidt and Beer have examined the products formed during the thermal decomposition of diacyl peroxides of the type [COgMe —(CHziw—CHz—COO] 2, where n = 1 and 3, in the presence of a series of organic compounds including pyridine and acridine. The products and yields of the reaction with some aromatic and heterocyclic compounds are shown in Table VI. As expected, acridine and... 

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