The Halogenation of Some Benzamides Takes Place Preferentially at the ortho, para Positions
✍ Scribed by Chang-Zhi Dong; Marc Julia; Jie Tang
- Publisher
- John Wiley and Sons
- Year
- 1998
- Tongue
- English
- Weight
- 233 KB
- Volume
- 1998
- Category
- Article
- ISSN
- 1434-193X
No coin nor oath required. For personal study only.
✦ Synopsis
The orientation of chlorination and bromination of N,N-atom. With large groups, the halogenation takes place fairly selectively at the ortho/para positions. disubstituted benzamides in aqueous acetic acid is strongly influenced by the nature of the alkyl groups at the nitrogen Table 1. Monochlorination of benzoic acid derivatives PhϪCOϪX
The chlorination of aromatic compounds has long been (1 mmol) with chlorine (80Ϫ100 bubbles/min) in 33% (v/v) aqueous known to take place at the side chain under free radical acetic acid (8 ml) at 50°C with reaction times 9 h [a] conditions and at the ring with electrophilic reagents. In the latter case, the orientation follows the classical Holleman X conv. (%) yield (%) o/m/p other products
rules [1] : some groups direct the substitution to the ortho,para positions, others to the meta positions [2] . However, in OH 41 100 3:97:0 Ϫ OMe 46 20 16:84:0 BzOH (25%), BzOCH 2 Cl some cases, the results are not always so clear-cut. In the (52%) course of other work, it became apparent that whereas ben-Cl 100 0 Ϫ BzOH (76%), m-Cl-BzOH (24%) zoic acid, its esters, and benzamide itself undergo electro-NH 2 100 trace Ϫ BzOH (66%), m-ClBzOH philic substitution fairly selectively at their meta positions, (28%)
N,N-disubstituted benzamides can behave very differently, NHEt 34 63 35:46:19 BzOH (23%) NHiPr 66 84 41:48:11 dichloro (9% ) showing once again that caution must be exercised in at-NHtBu 73 85 35:46:19 dichloro (10%) tempting to predict the course of a reaction. NMe 2 78 73 48:28:24 dichloro (9%) NEt 2 89 68 39:26:35 BzNHEt (10%), Cl-BzNHEt (9%, o/m/p ϭ Chlorination 29:33:38), dichloro (5%) NiPr 2 100 82 47:11:42 dichloro (12%) [b] , BzNHiPr
The ring chlorination of aromatics has been extensively (< 4%), BzOH (< 4%) investigated. Typically, chlorine in glacial acetic acid is used DMP