Preparative synthesis of N-benzyl-tert-butylamine

Abstract

N-Benzyl-tert-butylamine is used as starting compound in the synthesis of drugs and catalytic systems for polymerization of olefins, blocking agent for biuret groups in polyisocyanate compositions, and adsorbent of carbon dioxide from gas systems [1]. N-alkylbenzylamines I can be synthesized in two steps (Scheme 1) including condensation of benzaldehyde (II) with alkylamines III in lower aliphatic alcohols (C1–C4) without separation of water and subsequent hydrogenation of Schiff base IV in the presence of transition metal catalysts [2]. containing catalysts was accompanied by side hydrolytic processes, leading to the formation of up to 8% of benzyl alcohol (V) and up to 9% of toluene (VI) (Scheme 2). Apart from inefficient expenditure of the initial compounds, these side processes impair the purity of the target product (compound Ia). Though toluene (VI) can readily be removed by fractional distillation, benzyl alcohol (V) and N-benzyl-tert-butylamine (Ia) have similar boiling points, 99.5°C [3] and 100°C [4] at 17 mm, respectively. Owing to the presence of benzyl alcohol among the products, the concentration of the main substance in the target amine cannot exceed 90% without using special expensive separation methods. Benzyl alcohol is formed with participation of water liberated in the condensation leading to N-benzylidene-tert-butylamine (IVa), whereas dehydration of an alcoholic solution containing compound IVa is a laborious and energy-consuming process. We have found a simple and effective solution of the above problem. It implies synthesis of Schiff base IVa under solvent-free conditions with separation of most liberated water (no less than 90% of the theoretical amount) immediately after the condensation of benzaldehyde with tert-butylamine. The hydrogenation of Schiff base IVa is also carried out in the absence of Scheme 1. ISSN 1070-4280, Russian Journal of Organic Chemistry, 2009, Vol. 45, No. 12, pp. 1866–1867. © Pleiades Publishing, Ltd., 2009. Original Russian Text © A.G. Bazanov, A.F. Timofeev, N.G. Zubritskaya, 2009, published in Zhurnal Organicheskoi Khimii, 2009, Vol. 45, No. 12, pp. 1867–1868.