The heterolytic chlorination of 1-arylnaphthalene (aryl = 1(p-nitrophenyl), (p-chlorophenyl), 1-phenyl, and 1(p-methylphenyl) ) yields the appropriate 1-aryl-r-1,c-2,t-3,t-4-tetrachloro-1,2,3,4-tetrahydronaphthalene as the major product of addition. The 1H n.m.r. spectra of these compounds show that there is no significant change in the conformation adopted in solution accompanying the change in the para-substituent. The major product of the alkaline dehydrochlorination of each of these tetrachlorides using sodium methoxide in methanol-acetone (80:20 v/v) or benzene-methanol (75:25 v/v) is the 1-aryl-2,3-dichloronaphthalene. The first stage of the reaction is rate-controlling and both stages appear to be bimolecular. The observed rate-coefficients have been dissected to derive rates for the two competing elimination processes involving either initial loss of the 4-chlorine and 3-hydrogen or of the 1-chlorine and 2-hydrogen. The value of the Hammett reaction constant for the first of these processes was found to be 0.60 in methanol-acetone and 0.85 in benzene-methanol. The corresponding values for the second process were found to be 1.48 and 1.58. Both these results indicate that the effect of substituents in stabilizing the incipient negative charge developing at the β –carbon in the transition state is an important feature of the elimination processes involved. A slow, unimolecular solvolysis at the 1-chlorine has been observed with 1-Ph-NTC and 1(p-Me-Ph)NTC in methanol-acetone. It is proposed that the major product of this solvolysis results from the replacement of the 1-chlorine by a methoxy-group with retention of configuration. In contrast, the major product of solvolysis assisted by silver(I) ions is that possessing the inverted configuration. Alkaline dehydrochlorination of the methoxy-substituted compounds derived from 1(p-Me-Ph)NTC leads to fully aromatic products. This requires the elimination of the components of a molecule of methanol under comparatively mild alkaline conditions. Dehydrochlorination from the 1-arylnaphthalene tetrachlorides promoted by aluminium chloride in carbon disulphide at reflux temperature results in a mixture of the 1-aryl-2,3- and 2,4-dichloro- products. The proportion of 2,4-dichloro- product varies from 49% (1(p-NO2-Ph)NTC) to 65% (1-Ph-NTC).
| Identifer | oai:union.ndltd.org:ADTP/276025 |
| Date | January 1976 |
| Creators | Bedford, Keith R. (Keith Richard), 1951- |
| Publisher | ResearchSpace@Auckland |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated., http://researchspace.auckland.ac.nz/docs/uoa-docs/rights.htm, Copyright: The author |
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