Acid strength aliphatic acids

This explanation is probably applicable to the results recorded by Paesy, who found that with the homologous aliphatic acids the strength of the odour—as measured by the reciprocal of the smallest quantity that could be perceived—of formic acid is comparatively small, a maximum is reached with butyric acid and after diminution to the weak oenanthic acid, another maximum is reached with pelargonic acid, thereafter the odour diminishes very rapidly. 

The effect of introducing electron-withdrawing substituents into simple aliphatic acids is more marked. Thus halogen, with an inductive effect acting in the opposite direction to alkyl, might be expected to increase the strength of an acid so substituted, and this is indeed observed as pKa values show ... 

Other electron-withdrawing groups, e.g. R3N , CN, N02, SOzR, CO, C02R increase the strength of simple aliphatic acids, as also do... 

Many other linear Gibbs energy relationships have been proposed for example, the acid strengths of aliphatic compounds can be correlated using the "Taft polar substituent constants" o. ... 

Exercise 18-7 Fluoroethanoic acid is only about twice as acidic as chloroethanoic acid, even though fluorine is much more electronegative than chlorine (Section 10-4B). The lengths of aliphatic C-F bonds are about 1.38 A, whereas those of C-CI bonds are 1.78 A How could this difference in bond lengths tend to compensate for the differences in electronegativity between chlorine and fluorine and make the acids similar in strength ... 

The rate of reaction of DCC with aliphatic acids in THF depends on the acid strength, i.e., chloroacetic acid reacts considerably faster than acetic acid." It was also found that the higher the acid strength, the higher the yields of anhydride and urea. The reaction exhibits first order kinetics both in acid and in carbodiimide, and the rate determining step is the formation of the O-acylurea." Solvent effects are also observed in the reaction of DCC with acetic acid. The reaction rates are highest in THF, and the proportion of N-acylurea is also the greatest in THF." ... 

Polyesters containing long-chain unbranched glycols have the highest impact strength. This property also increases with the increase in the chain length of aliphatic acids. 

Further use of this oxidant to produce a number of poly nitro aromatics was reported by Nielsen and co-workers [71] in their remarkable paper. The authors also reviewed work on the other oxidants used to pass from HN to NO Caro acid, peracetic, permaleic, m-chloroperbenzoic and perbenzoic acids. They pointed out that the power of the oxidant is proportional to the acid strength of deoxy peracid. Peracetic and m-chloroperbenzoic acids are suitable for the oxidation of aliphatic primary amines, whereas peracetic, peroxytrifluoroacetic and peroxymaleic acids are best for the oxidation of ring substituted anilines. Potassium persulphate in sulphuric acid was also used successfully [71 ]. 

The reaction of ylides with saturated aliphatic alkyl halides (like methyl iodide, ethyl iodide etc.) usually stops at the stage of the alkylated salt because the +/ effect of the aliphatic substituent causes the resulting salt to be a weaker acid than the conjugated salt of the original ylide (which would result in the course of a transylidation reaction). However since partial transylidation also occurs between al-kylidenephosphoranes and phosphonium salts with equal or not very different base and acid strength, mixtures may result from Ae reaction with saturated aliphatic alkyl halides. At this point it should be mentioned that the synthesis of dialkylated ylides via the salt method is also difficult since the preparation of the necessary phosphonium salt is accompanied by -elimination. The successful synthesis of dialkylated ylides may be achieved by fluoride ion induced desilylation of a-trimethylsilylphosphonium salts (see equation 18). There is no doubt about the course of ylide alkylation in cases where the inductive effect of the new substituent leads to complete transylidation (e.g. equation 54). ... 

According to Tanaka and Fritz [9], comparably low background conductivities were obtained with benzoic acid as the eluent, because benzoic acid is only partly dissociated. However, the acid strength of a dilute benzoic acid solution is sufficient to elute aliphatic carboxylic acids with a good peak shape. 

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