Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Toluenes, substituted

The ammoxidation of toluenes substituted with electron-donating groups, for example hydroxy- and alkoxy-substituted toluenes is rather less selective. However, under carefully chosen conditions (choice of the catalyst, feed composition, reaction conditions) adequate yields of nitriles can be achieved. Stabihty of the catalyst performances is typically an issue. [Pg.794]

Toluenes substituted with chloro, bromo, fluoro, or cyano groups can be dichlorinated or dibrominated and the resulting benzal halides hydrolyzed directly to the corresponding aldehydes in the presence of calcium carbonate or sulfuric acid (50-70%). o- and p-Xylene have been converted to the corresponding dialdehydes. ° In the halogenation of certain cresols, the carbonate or acetate esters are used in order to prevent nuclear halogenation. ... [Pg.594]

In toluene, substitution is thus faster than meta substitution because... [Pg.362]

Huber and Schwoererdescribe e.s.r. experiments which show the existence of quintet states (S = 2) after u.v. irradiation at 4.5 K in perdeuteriated / -toluene-substituted diacetylene. Nine e.s.r. transitions per quintet were detected and were attributed to bicarbenes of short oligomers. E.s.r. has also been applied to the study of photochemical reactions of fluoro-substituted ketones with amines, tetraphenylborates, and organometals." ... [Pg.104]

It is also to he noted that ortho and para substitution often occur together in the same molecule, so that the group R enters the para and also both the ortho positions thus both aniline and phenol on bromination readily give symmetric (2,4,6) tribromo-compounds (p. 165), while both toluene and phenol on nitration readily give the symmetric trinitro-derivatives (p. 170). [Pg.159]

Amine B.P. M.P., 20 20 Benzene- sulphonamlde />-Toluene- sulphoiuunide Phenyl- thiourea a-Naphthyl- thlourea Pierate iV-Substituted Phthallmlde Benzamide... [Pg.424]

This h)rpothesis has, however, been supported. The o p-ratio in chlorobenzene was found to be lower when acetic anhydride was the solvent, than when nitric acid or mixed acids were used. The ratio was still further reduced by the introduction into the solution of an even less polar solvent such as carbon tetrachloride, and was increased by the addition of a polar solvent such as acetonitrile. The orientation of substitution in toluene in which the substituent does not posses a strong dipole was found to be independent of the conditions used. The author... [Pg.93]

If acetoxylation were a conventional electrophilic substitution it is hard to understand why it is not more generally observed in nitration in acetic anhydride. The acetoxylating species is supposed to be very much more selective than the nitrating species, and therefore compared with the situation in (say) toluene in which the ratio of acetoxylation to nitration is small, the introduction of activating substituents into the aromatic nucleus should lead to an increase in the importance of acetoxylation relative to nitration. This is, in fact, observed in the limited range of the alkylbenzenes, although the apparently severe steric requirement of the acetoxylation species is a complicating feature. The failure to observe acetoxylation in the reactions of compounds more reactive than 2-xylene has been attributed to the incursion of another mechan-104... [Pg.104]

If, on the other hand, the encounter pair were an oriented structure, positional selectivity could be retained for a different reason and in a different quantitative sense. Thus, a monosubstituted benzene derivative in which the substituent was sufficiently powerfully activating would react with the electrophile to give three different encounter pairs two of these would more readily proceed to the substitution products than to the starting materials, whilst the third might more readily break up than go to products. In the limit the first two would be giving substitution at the encounter rate and, in the absence of steric effects, products in the statistical ratio whilst the third would not. If we consider particular cases, there is nothing in the rather inadequate data available to discourage the view that, for example, in the cases of toluene or phenol, which in sulphuric acid are nitrated at or near the encounter rate, the... [Pg.119]

TABLE 7.1 Partial rate factors for some electrophilic substitutions of toluene... [Pg.124]

Brown noticed that the reactivities of toluene relative to benzene in aromatic substitutions were proportional to the ratios in which toluene underwent p- and -substitutions. This point is illustrated in table 7.3. [Pg.140]

Relative rates and isomer ratios for substitution in benzene and toluene ... [Pg.140]

The selectivity of an electrophile, measured by the extent to which it discriminated either between benzene and toluene, or between the meta- and ara-positions in toluene, was considered to be related to its reactivity. Thus, powerful electrophiles, of which the species operating in Friedel-Crafts alkylation reactions were considered to be examples, would be less able to distinguish between compounds and positions than a weakly electrophilic reagent. The ultimate electrophilic species would be entirely insensitive to the differences between compounds and positions, and would bring about reaction in the statistical ratio of the various sites for substitution available to it. The idea has gained wide acceptance that the electrophiles operative in reactions which have low selectivity factors Sf) or reaction constants (p+), are intrinsically more reactive than the effective electrophiles in reactions which have higher values of these parameters. However, there are several aspects of this supposed relationship which merit discussion. [Pg.141]

Kinetic data are available for the nitration of a series of p-alkylphenyl trimethylammonium ions over a range of acidities in sulphuric acid. - The following table shows how p-methyl and p-tert-h xty augment the reactivity of the position ortho to them. Comparison with table 9.1 shows how very much more powerfully both the methyl and the tert-butyl group assist substitution into these strongly deactivated cations than they do at the o-positions in toluene and ferf-butylbenzene. Analysis of these results, and comparison with those for chlorination and bromination, shows that even in these highly deactivated cations, as in the nitration of alkylbenzenes ( 9.1.1), the alkyl groups still release electrons in the inductive order. In view of the comparisons just... [Pg.185]

Under certain conditions, the /(-substitution products are obtained as major products[66]. Methyl vinyl ether reacts with bromonitrobenzene to give the f-methoxystyiene 64 in good yield in toluene at 120 "C by using Pd on carbon as... [Pg.137]

Cycloaddition of COj with the dimethyl-substituted methylenecyclopropane 75 proceeds smoothly above 100 °C under pressure, yielding the five-membered ring lactone 76. The regiocheraistry of this reaction is different from that of above-mentioned diphenyl-substituted methylenecyclopropanes 66 and 67[61], This allylic lactone 76 is another source of trimethylenemethane when it is treated with Pd(0) catalyst coordinated by dppe in refluxing toluene to generate 77, and its reaction with aldehydes or ketones affords the 3-methylenetetrahy-drofuran derivative 78 as expected for this intermediate. Also, the lactone 76 reacts with a, /3-unsaturated carbonyl compounds. The reaction of coumarin (79) with 76 to give the chroman-2-one derivative 80 is an example[62]. [Pg.522]

Three products are possible from nitration of toluene o mtrotoluene m nitro toluene and p mtrotoluene All are formed but not m equal amounts Together the ortho and para substituted isomers make up 97% of the product mixture the meta only 3%... [Pg.488]

Because substitution in toluene occurs primarily at positions ortho and para to methyl we say that a methyl substituent is an ortho, para director... [Pg.489]

Two isomeric arynes give the three isomeric substitution products formed from m chloro toluene... [Pg.985]


See other pages where Toluenes, substituted is mentioned: [Pg.207]    [Pg.562]    [Pg.103]    [Pg.1182]    [Pg.41]    [Pg.441]    [Pg.562]    [Pg.40]    [Pg.939]    [Pg.1077]    [Pg.46]    [Pg.513]    [Pg.207]    [Pg.562]    [Pg.103]    [Pg.1182]    [Pg.41]    [Pg.441]    [Pg.562]    [Pg.40]    [Pg.939]    [Pg.1077]    [Pg.46]    [Pg.513]    [Pg.401]    [Pg.401]    [Pg.192]    [Pg.93]    [Pg.117]    [Pg.123]    [Pg.184]    [Pg.240]    [Pg.242]    [Pg.242]    [Pg.75]    [Pg.77]    [Pg.218]    [Pg.488]    [Pg.490]   
See also in sourсe #XX -- [ Pg.41 , Pg.42 ]




SEARCH



Ammoxidation of Substituted Toluenes

Halogen-substituted Toluenes

Hydroxy- and Alkoxy-substituted Toluenes

Methyl-substituted Toluenes

Substituted toluenes, benzylic metallation

Toluene Chlorine substitution products

Toluene Dioxygenase Indigo or Prostaglandins from Substituted Benzenes via cis-Dihydrodiols

Toluene electrophilic aromatic substitution

Toluene electrophilic aromatic substitution, product

Toluene electrophilic substitution

Toluene meta substitution

Toluene para substitution

Toluene substitution pattern

Toluene substitution reactions

Toluene, dipole moment substitution

Toluene, multi-substituted

Toluene, other-substituted

© 2024 chempedia.info