Benzonitrile, hydrolysis benzamide

The mechanism for acidic hydrolysis of a nitrile resembles the basic hydrolysis, except that the nitrile is first protonated, activating it toward attack by a weak nucleophile (water). Under acidic conditions, the proton transfer (tautomerism) involves protonation on nitrogen followed by deprotonation on oxygen. Propose a mechanism for the acid-catalyzed hydrolysis of benzonitrile to benzamide. 

Benzamide from Benzonitrile. (A) Although benzonitrile when boiled with 70% sulphuric acid undergoes ready hydrolysis to benzoic acid (see above), treatment with hot 90% sulphuric acid gives the intermediate benzamide. This difference arises partly from the difference in temperature employed, but also... 

Capon et al., 1978. No reference bimolecular reaction is available, but o-cyanobenzoic acid is hydrolysed over 10 times faster than phthalamic acid (A.3.9), although benzonitrile is less reactive than benzamide towards acid hydrolysis. [Rate constants for hydrolysis are (1-2) x 10 s for benzonitrile in 1 M acid (Hyland and O Connor, 1973) and 3.5 x 10-4 dm3 mol-1 s 1 for benzamide (Bender et al., 1958), both measured at 100°]... 

It is known that A-chloromethyl benzamide 234 (i.e. derivative 216 of formaldehyde) reacts with benzonitrile in the presence of tin tetrachloride to yield 4//-1,3,5-oxadiazinium salt 235, the hydrolysis of which gives bis-amide 236131 (equation 67). 

Roberts and Whiting developed a method for effecting the anhydrous hydrolysis of esters and nitriles in DMSO. A solution of sodium methylsulfinylmethide is prepared from sodium hydride and DMSO and titrated with a solution of an appropriate amount of water in DMSO, using triphenylmethane as indicator. This produces a fine suspension of sodium hydroxide which hydrolyzes ethyl benzoate very rapidly at room temperature. As compared with reactions in hydroxylic solvents, rates are enhanced by a factor of 10 -10 . Benzonitrile is hydrolyzed to benzamide. Methyl and ethyl mesitoates are hydrolyzed readily at 25°. 

Alkyl and aryl nitriles readily hydrolyze when submitted to NCW conditions. The hydrolysis is a multistep sequence as shown in Fig. 9.26. For instance, Katritzky et al. have reported that benzonitrile is converted to benzamide and benzoic acid at 250°C over a period of 5 days, and they conclude that the amide and the acid were in equilibrium. Under these conditions some decarboxylation can also occur. An et al. have reported the product distribution for the hydrolysis of benzonitrile as a function of time and temperature. Specifically, the ratio of benzamide to benzoic acid varied as follows after 1 h at 250°C, the distribution was 5 4. However, at 280°C after 1 h, the ratio was 1 1, and became 1 25 when the reaction time was extended to 6 h. Alkylnitriles exhibit similar behaviors Siskin et ah reported that at 250°C for 2.5 days decanonitrile quantitatively yields two major products, decanoic acid and decanoamide. When octanenitrile was hydrolyzed to octanoic acid amide and octanoic acid, the reaction was slightly slower than that ofbenzonitrile. Only 29% conversion took place in 1 h at 290°C. The limited solubility of octanenitrile in water, even in NCW conditions, was suggested as a possible factor for the slow reaction. Again the product distribution was dependent on the residence time and the temperature. 

Moreover, an aerobic oxidative decarboxylative ammoxidation of phenylacetic acids and a-hydroxyphenylacetic acids to primary benzamides was realized with CU2O catalyst [28] (Scheme 3.10). The C(C=0)-N bond was formed with NH3 as nitrogen source and O2 as the sole terminal oxidant. Benzonitrile which is generated from phenylacetic acid through decarboxylation and ammoxidation with ammonia is the key intermediate for this transformation. It could convert into benzamide through ammonolysis and hydrolysis. A variety of primary benzamides could be prepared in 36-85 % yields form the corresponding acid. 

---