Study On The Synthesis Of Protocatechuic Aldehyde And 3,4-Dihydroxybenzonitrile From Vanillin

Protocatechuic aldehyde and 3,4-dihydroxybenzonitrile are important organic intermediates,which are widely used in chemical and pharmaceutical industries. Traditional methods forpreparing these intermediates suffer from serious drawbacks like long reaction time, severeenvironment pollution, high production costs, etc. Following"green chemistry"principles,high efficiency and clean synthesis of protocatechuic aldehyde and 3,4-dihydroxybenzonitrilewere realized in this paper.The green solvents were screened and the reaction conditions were optimized for thesynthesis of protocatechuic aldehyde from vanillin. High yield of protocatechuic aldehyde(95.7%) was obtained with good purity (99.9%). And reaction time was cut to 10 h, much shorterthan the literature values of 28 h. Thus improved manufacturing efficiency and reduced energyconsumption. Moreover, the reaction mechanism for the synthesis of protocatechuic aldehydefrom vanillin was investigated by React IRTM IC10. The result showed that AlCl₃ first attackedon phenol hydroxyl of vanillin and formed coordinate bond of Al-O with phenol hydroxyl.Subsequently, pyridine could easily attack on -OCH₃ and then bonded with Al-O at theortho-position of benzene ring, which weakened the bond strength of O-CH₃. Thereby H+ couldattack O-CH₃ and removed -CH₃, and then hydrolyzed into protocatechuic aldehyde.The preparation process for 3,4-dihydroxybenzonitrile from protocatechuic aldehyde andhydroxylamine-O-sulfonic acid was investigated, and the qualitative and quantitative analysismethods were established. Under the optimized reaction conditions, the3,4-dihydroxybenzonitrile yield was up to 91.0% and the purity was 99.6%. Additionally, thepossibility of using hydroxylamine hydrochloride or hydroxylamine sulfate as reactant wasstudied instead of hydroxylamine-O-sulfonic acid. The results showed that the protocatechuicaldehyde was converted completely, and two by-products of 3,4-dihydroxybenzaldoxime and3,4-dihydroxybenzamide were obtained. 3,4-dihydroxybenzonitrile was obtained only in thepresence of formic acid, whereas the yield of product was lower. The reaction mechanism ofprotocatechuic aldehyde with hydroxylamine-O-sulfonic acid was presumed. The3,4-dihydroxybenzaldoxime was obtained by the nucleophilic addition reaction of the carbonyl of protocatechuic aldehyde and hydroxylamine. Under the acid condition, N-O bands werebroken when oxygen atoms of hydroxyl coordinate with the H⁺ formed coordination bond, andthen the water could be successfully removed. Finally, 3,4-dihydroxybenzonitrile was obtained.