Chem. J. Chinese Universities ›› 1995, Vol. 16 ›› Issue (10): 1544.
• Articles • Previous Articles Next Articles
YU Zhong-Heng, ZHANG WEN-Chun, JIANG Ming-Qian, DAI Cui-Chen
Received:
Revised:
Online:
Published:
Abstract: In order to study substituent effects on the substitution reactions of 10 multi-sub-stituted benzene, (这里有图片199510-1549-1.gif)the relative yields of the products from their nitration and bromination in different solventsare investigated.The esteric group(X=-CH2OAc) of compound 2(R1=t-Bu and R2=-Me)vields 60%-60% ipso-product 2b(X=NO2,R1=t-Bu and R2=Me) for the nitration in a solution of 65% nitric acid and Ac2O, and 84% ipso-roduct 3b(X=Br, R1=-t-Bu and R2=Me)for the bromination in a solution of 65% nitric acid,NaBr and EtOH. Under the same conditions.the esteric group(X=CH2ONO2) of the compound 4(R1=t-Bu and R2=Me)gives 30% 2band 95% 3brespectively. An interesting bromination of compound 3(R1=t-Bu,R2=Me and X=CH2Br)in a solution of 65% nitric acid and EtOH yields 95% ipso-product 3b. Firstiy, this bromination proceeds practically through a intermediate 4 which resulted from the replacement of Br-by NO3- and then the esteric group(X=CH2ONO2)of intermediate 4 is substituted by Br2resulting from the oxidation of Br-by nitric acid. No matter what the alkyl groups,R1 and R2, are, no ipso-product was found from the nitration of thecompounds,where X=-CH2Cl and-CH2Br in acetic anhydride,which means that the esteric groups,-CH2OAc and-CH2ONO2,and only them are ipso-directors in the case of thepresented compounds, The esteric groups would seem to make it possible for the reactions toproceed through the six-membered cyclic transition states such as: Steric effect of the alkyl groups helps the esteric group to yield ipso-product.the group,X=-CH2OAc, of compounds 8(R1=R2=Me) gives only 5% ipso-product for the nitration.
Key words: Multi-substituted benzene, Ipso nitration, Ipso bromination, Six-membered cyclic transition state
TrendMD:
YU Zhong-Heng, ZHANG WEN-Chun, JIANG Ming-Qian, DAI Cui-Chen . IPSO Nitration and Bromination of the Multi-substituted Benzene[J]. Chem. J. Chinese Universities, 1995, 16(10): 1544.
0 / / Recommend
Add to citation manager EndNote|Ris|BibTeX
URL: http://www.cjcu.jlu.edu.cn/EN/
http://www.cjcu.jlu.edu.cn/EN/Y1995/V16/I10/1544