Decarboxylation of aliphatic acids

The kinetic study of the decarboxylation of aliphatic acids in co-oxidation with cumene showed the following two chemical channels of C02 production [104],... 

Decarboxylation of aliphatic acids by means of their derived 0-acyl thiohydioxaniates in die presence of an electron deficient terminal alkene results in the overall addition of an alkyl radical and a 2-pyri dylthiyl radical across the double bond (equation 48). 

The decarboxylation of aliphatic acids may take place as an aliphatic electrophilic substitution but also in some cases can be regarded as an elimination reaction using a cyclic mechanism as described in Section 2.1. 

Another example of this type of reaction is the decarboxylation of aliphatic acids. For the decarboxylation to proceed easily there must be an electron withdrawing group capable of stabilising the negative charge. An example would be an a-ketoacid, e.g. RCOCOOH. Suggest a mechanism for this reaction. 

Bicyclo [2.1.1] hexane-5-carbonyl chloride added during 1 hr. with ice-saltcooling to a stirred mixture of ferf-butyl hydroperoxide, dry pyridine and p-cymene, stirring and cooling continued for an additional hr., poured onto ice, the p-cymene phase containing ferf-butyl bicyclo [2.1.1] hexane-5-peroxy-carboxylate separated, washed, dried, and heated in a wax bath at 115-130 until GOg-evolution ceases after 2 hrs., then distilled until the head temp, reaches 176° (p-cymene) bicyclo [2.1.1] hexane. Y 45%.—This is a convenient method for the decarboxylation of aliphatic acids. F. e. with lower yield s. K. B. Wiberg, B. R. Lowry, and T. H. Golby, Am. Soc. 83, 3998 (1961). 

Mehrotra RN (1981) Kinetics and mechanisms of redox reactions in aqueous solution. Part 7. Decarboxylation of aliphatic acids by aquasilver(II) ions. J Chem Soc Dalton Trans 897-901... 

Mittal L, Mittal JP, Hayon E (1973) Photo-induced decarboxylation of aliphatic acids and esters in solution. Dependence upon state of protonation of the carboxyl group. J Phys Chem 77 1482-1487... 

Secondary aliphatic amines reacted readily with mercaptoaldimines (279), which could be prepared readily by the action of Na/NH3 on the aldehyde diacetals (278). The resulting N,N- dialkyl derivatives (280) were alkylated on sulfur by a-halocarbonyl compounds such as bromoacetic acid the resulting products (281) underwent spontaneous ring closure and aromatization via loss of the secondary amine to yield the acids (282 Scheme 97). Decarboxylation of the acids (282) furnished the substituted thieno[2,3-6 ]thiophenes (283). The use of other a-halocarbonyl compounds, such as bromoacetone or phenacyl bromide for the alkylation, led to the formation of the 2-acetyl or 2-benzoyl derivatives, (284) and (285) respectively (76AHC(19)123). 

The persulfate ion S2OI-, with or without various transition metal ions, is a particularly effective oxidant, especially for the decarboxylation of carboxylic acids.535 In the presence of silver(I), persulfate oxidation to silver(II) readily occurs and for aliphatic carboxylic acids the decarboxylation mechanism given in Scheme 4 has been established. The aliphatic radicals produced may then disproportionate, abstract hydrogen or be further oxidized to an alcohol. In... 

Aliphatic hydrocarbons such as n-alkanes and n-alkenes have been successfully used to distinguish between algal, bacterial, and terrestrial sources of carbon in estuarine/coastal systems (Yunker et al., 1991, 1993, 1995 Canuel et al., 1997). Saturated aliphatic hydrocarbons are considered to be alkanes (or paraffins) and nonsaturated hydrocarbons which exhibit one or more double bonds are called alkenes (or olefins)—as indicated in the simple structures of hexadecane and 1,3-butadiene, respectively (figure 9.7). It should also be noted that, n-alkanes tend to be odd-numbered as they result from enzymatic decarboxylation of fatty acids. Long-chain n-alkanes (LCH) (e.g., C27, C29, and C31) are generally considered to be terrestrially derived, originating from epicuticular waxes... 

Silver-catalyzed persulfate decarboxylation of carboxylic acids in chloroform provides the noralkane in modest to good yields. Only a limited number of examples with simple aliphatic carboxylic acids are known. 

The oxidative decarboxylation of aliphatic carboxylic acids is best achieved by treatment of the acid with LTA in benzene, in the presence of a catalytic amount of copper(II) acetate. The latter serves to trap the radical intermediate and so bring about elimination, possibly through a six-membered transition state. Primary carboxylic acids lead to terminal alkenes, indicating that carbocations are probably not involved. The reaction has been reviewed. The synthesis of an optically pure derivative of L-vinylglycine from L-aspartic acid (equation 14) is illustrative. The same transformation has also been effected with sodium persulfate and catalytic quantities of silver nitrate and copper(II) sulfate, and with the combination of iodosylbenzene diacetate and copper(II) acetate. ... 

As a preparative method the direct decarboxylation of olefinic acids is almost limited to the formation of styrenes and stilbenes from substituted cinnamic acids. Thermal decomposition of cinnamic acid gives styrene (41%). The yield is nearly quantitative if the reaction is carried out in quinoline at 220° in the presence of a copper catalyst. The yields of substituted styrenes where the aryl radical contains halo, methoxyl, aldehyde, cyano, and nitro groups are in the range of 30-76%. cis-Stilbene and cis-p-nitrostilbene are prepared in this way from the corresponding a-phenylcinnamic acids (65%). One aliphatic compound worthy of mention is 2-ethoxypropene, prepared by heating -ethoxycro-tonic acid at 165° (91% yield). The mechanism of acid-catalyzed decarboxylations of this type has been studied. Isomerization of the double bond from the a,/5- to the /5, y-position before decarboxylation very likely occurs in many instances. ... 

Only moderate yields of hydrocarbon are obtained in this way from salts of aliphatic acids here the main side reaction is formation of the ketone by only partial decarboxylation. This ketone formation becomes the main reaction if the calcium salt is not mixed with an excess of lime but is submitted alone to dry distillation ... 

These compounds all closely resemble the corresponding benzene compounds in their reactivity because the carbonyl group cannot interact mesomerically with the ring nitrogen. The pyridine 2- (picolinic), 3- (nicotinic), and 4- (isonicotinic) acids exist almost entirely in their zwitterionic forms in aqueous solution they are slightly stronger acids than benzoic acid. Decarboxylation of picolinic acids is relatively easy and results in the transient formation of the same type of ylide which is responsible for specific proton a-exchange of pyridine in acid solution (see section 5.1.2. ). This transient ylide can be trapped by aromatic or aliphatic aldehydes in a reaction known as the Hammick reaction. As implied by this mechanism, quaternary salts of... 

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