Mesitoic acid

The kinetics of the sulphuric acid-catalysed decarboxylation of a range of alkyl substituted benzoic acids have been measured by Schubert et a/.634,635. The variation of rate coefficient with temperature for mesitoic acid is given in Table 206 and the value for the methyl ester shows that, at this acid concentration, the... 

The rates of decarboxylation of a range of 3-substituted mesitoic acids in 82.1 wt. % phosphoric and 83.0 wt. % sulphuric acids have been measured636 over a range of temperatures as indicated in Table 209, which gives the first-order rate coefficients together with the log A values and the energies, enthalpies, and entropies of activation calculated at 80 °C for sulphuric acid, and 119 °C for phosphoric acid these kinetic parameters are somewhat different from those... 

The other mechanism involving acyl cleavage is the AacI mechanism. This is rare, being found only where R is very bulky, so that bimolecular attack is sterically hindered, and only in ionizing solvents. The mechanism has been demonstrated for esters of 2,4,6-trimethylbenzoic acid (mesitoic acid). This acid depresses the freezing point of sulfuric acid four times as much as would be predicted from its molecular weight, which is evidence for the equilibrium... 

Phosphonoformic acid (85) decarboxylated in acid solution, and it was proposed that the uncatalysed reaction involved a simple decarboxylation of the zwitterion. The acid-catalysed reaction showed some kinetic similarity to that of mesitoic acid and an elimination of carbon dioxide as trihydroxymethylcarbonium ion was preferred. Participation of the trans vicinal phosphonyl group in the solvolysis of the halides (86) and (87) has been deduced from rate measurements. In the norbornene derivatives, the relative rates of loss of chloride from (87a) and (87b) were 5 x 10 1. 

Exactly the same considerations apply to the esterification of hindered acids (182) in the reverse direction. It will be noticed that this mechanism requires protonation on the less favoured (cf. p. 240) hydroxyl oxygen atom (185) to allow the formation of the acyl carbocationic intermediate (184). Apart from a number of R3C types, a very well known example is 2,4,6-trimethylbenzoic (mesitoic) acid (186), which will not esterify under ordinary acid-catalysis conditions—and nor will its esters (187) hydrolyse. Dissolving acid or ester in cone. H2S04 and pouring this solution into told alcohol or water, respectively, is. found to effect essentially quantitative esterification or hydrolysis as required the reaction proceeds via the acyl cation (188) ... 

This is essentially true, as is evidenced by the rates of esterification in alcoholic media of propan-l-ol with ethanoic acid [27] or of propan-2-ol with mesitoic acid [28], The absence of a specific microwave effect became apparent from several experiments carefully conducted in alcohols or in DMF under similar conditions but with microwave or classical heating [7]. 

The use of mesitoic acid esters has again been successfully employed by Burrows and Topping (1975) in the elucidation of intramolecular carbon acid participation. Under basic aqueous conditions, 2-acetylphenyl mesitoate [41] hydrolyses to yield mesitoic acid and 2-hydroxyacetophenone, reacting with intramolecular catalysis via the monoanion of the ketonic hydrate (see p. 192). However, in 47.5% aqueous ethanol containing potassium hydroxide, the reaction products from l-acetyl-2-naphthyl mesitoate [45] were found... 

Similar results have been obtained with substituted triphenylcarbinols in sulfuric acid.174 Some unsaturated hydrocarbons form carbonium ions by simple addition of a proton, as do some carboxylic acids.175-177 But other carboxylic acids behave like the triarylcarbinols, the most prominent example being mesitoic acid. 

Solutions containing ions give chemical reactions expected of the ions. For example, mesitoic acid, which resists esterification by other methods, is readily esterified when its sulfuric acid solution is poured into an alcohol.177... 

In some systems the acylium ion is formed reverisbly and to a detectable extent while in others, to be discussed in the next chapter, it is a hypothetical intermediate. The first evidence for a stable acylium ion was the fourfold depression of the freezing point of sulfuric acid by mesitoic acid.176 The presence of the acylium ion in the sulfuric acid solutions of carboxylic acids with fourfold depressed freezing points is confirmed chemically by the high yield of ester obtained on pouring the... 

A combination of steric and electrostatic factors is presumably decisive with regard to the form of the acid most stable in sulfuric acid solution. The simple protonated form XX of benzoic acid is stabilized by resonance structures sterically prohibited in mesitoic acids. The ortho methyl groups of mesitoic acid would interfere with a coplanar dihydroxymethylene group. On the other hand, the inductive and resonance effects of the methyl groups help stabilize the acylium ion form of mesitoic acid as in the formulae XXI. In the case of 2,4,6-tribromobenzoic acid the steric effect and its abetting electronic effects are not sufficient, and this acid behaves like benzoic acid.17 >177... 

Mesitoic acid, for example, will give the amine at 0°, while benzoic acid requires a temperature of 35° for the reaction to go at a convenient rate. Presumably the higher concentration of acylium ion in the former case reacts more rapidly than a lower concentration or a less reactive source of acyl groups in the latter case.286... 

After the addition is completed, the reaction mixture is refluxed for 1 hour and is then poured very cautiously with manual stirring onto a mixture of 2 kg. of crushed ice and 300 ml. of 12N hydrochloric acid in a 4-1. beaker. The mixture thus formed is extracted with three 250-ml. portions of carbon tetrachloride. The combined organic extracts are washed with two 500-ml. portions of water, and the acid is then extracted with 500 ml. of ice-cold 10% sodium hydroxide solution. The aqueous extract is then slowly added to 250 ml. of 6N hydrochloric acid. The suspension is cooled, and the mesitoic acid is separated by filtration, washed thoroughly with water, and dried. The colorless crude acid (m.p. 149-150°) weighs 106-124 g. (65-76%) (Note 4) and is sufficiently pure for most purposes (Note 5). 

Allylmagnesium bromide, 41, 49 reaction with acrolein, 41,49 5-AUyl-l,2,3,4,5-pentachlorocydopen-tadiene, 43, 92 Allyltriphenyltin, 41, 31 reaction with phenyllithium, 41, 30 Aluminum chloride, as catalyst, for isomerization, 42, 9 for nuclear bromination and chlorination of aromatic aldehydes and ketones, 40,9 as Friedel-Crafts catalyst, 41, 1 in preparation of mesitoic acid, 44, 70 in preparation of 2u-thiohomo-phthalimide, 44, 91... 

Mesitoic acid has been prepared by carbonation of mesityl-magnesium bromide 2-4 by hydrolysis of its amide prepared by condensation of mesitylene with carbamyl chloride under the influence of aluminum chloride 6 by oxidation of isodurene with dilute nitric acid 6-7 by distillation of 2,4,6-trimethylmandelic acid (low yield) 8 by dry distillation of 2,4,6-trimethyIphenyl-glyoxylic acid 9 by oxidation of the latter with potassium permanganate 10 and by treating 2,4,6-trimethylphenylglyoxylic acid with concentrated sulfuric acid in the cold11 or with heating.12... 

The method described in this preparation of mesitoic acid avoids the preparation of bromomesitylene,13 and the yield of acid is essentially the same as that from the two-step synthesis.2-13 This procedure appears to be general and can be used to prepare such acids as a- and /3-naphthoic acids,14 cumenecarboxylic acid, 2,5-dimethylbcnzoic acid, and durenecarboxylic acid. Carboxylic acids could not be obtained from benzothiophene, vera-trole, -dimethoxybenzene, and ferrocene under the conditions of this reaction. Although there has been no exhaustive study, this procedure is probably applicable to a variety of aromatic compounds, especially alkylated aromatics. Aromatic compounds which readily undergo oxidation, e.g., ferrocene, catechol, and hydroquinone, do not lend themselves to this method. 

Certain preparations—mesitoic acid, 7-t-butoxynorbornadi-ene, cyclopentanecarboxaldehyde, t-butyl azidoformate, indole-... 

Freezing point depression benzoic acid, 242 ketones, 103 mesitoic acid, 243 nitric acid, 134 Friedel-Crafts reaction acylation, 143 acylium ions in, 144 alkylation, 141... 

In a comparable solution of benzoic acid the freezing point is depressed only twice the predicted amount, indicating only a normal acid-base reaction. Further, a sulfuric acid solution of methyl mesitoate when poured into water gave mesitoic acid, while a similar solution of methyl benzoate similarly treated did not.534 The AacI mechanism is also found when acetates of phenols or of primary alcohols are hydrolyzed in concentrated (more than 90%) H2SO4 (the mechanism under the more usual dilute acid conditions is the normal Aac2).535... 

There are actually three reactions called by the name Schmidt reaction, involving the addition of hydrazoic acid to carboxylic acids, aldehydes and ketones, and alcohols and olefins.227 The most common is the reaction with carboxylic acids, illustrated above.228 Sulfuric acid is the most common catalyst, but Lewis acids have also been used. Good results are obtained for aliphatic R, especially for long chains. When R is aryl, the yields are variable, being best for sterically hindered compounds like mesitoic acid. This method has the advantage over 8-14 and 8-15 that it is just one laboratory step from the acid to the amine, but conditions are more drastic.229 Under the acid conditions employed, the isocyanate is virtually never isolated. 

Trimethylbenzoic acid (mesitoic acid) [480-63-7] M 164.2, m 155°. Crystd from water, ligroin or carbon tetrachloride [Ohwada et al. JACS 108 3029 1986. ... 

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