Chlorine derivatives of toluene

The chlorination of toluene can be carried out in the side chain and in the aromatic nucleus both product groups are of commercial significance, although side-chain-chlorinated toluenes are predominant in terms of quantity. 

The two types of reaction follow different reaction mechanisms. Side-chain chlorination occurs by a radical chain reaction mechanism, nuclear chlorination by electrophilic substitution. 

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The ring-chlorinated derivatives of toluene form a group of stable, industrially important compounds. Many chlorotoluene isomers can be prepared by direct chlorination. Other chlorotoluenes are prepared by indirect routes involving the replacement of amino, hydroxyl, chlorosulfonyl, and nitro groups by chlorine and the use of substituents, such as nitro, amino, and sulfonic acid, to orient substitution followed by their removal from the ring. 

In some cases this reaction takes place with water alone but usually some other substance is present e.g., calcium hydroxide or carbonate, potassium hydroxide, metallic iron or iron salts which actsasacatalizer. The mono-chlorine derivative of toluene and other benzene homologues may also be used for preparing the aldehydes. In this case the reaction is in two steps, first, reaction with water yielding the alcohol, and second. 

Ring-Substituted Derivatives The ring-chlorinated derivatives of benzyl chloride, benzal chloride, and benzotrichloride are produced by the direct side-chain chlorination of the corresponding chlorinated toluenes or by one of several indirect routes if the required chlorotoluene is not readily available. Physical constants of the main ring-chlorinated derivatives of benzyl chloride, benzal chloride, and benzotrichloride are given in Table 4. 

Write the graphic formulas of the dichloro derivatives of toluene. Include the compounds containing chlorine in the methyl group. 

Whereas the nitro derivatives of benzene are produced by electrophilic aromatic substitution, further important derivatives of toluene are predominantly obtained through reactions of the methyl group they include the production of oxidation products such as benzoic acid and the side-chain chlorinated toluene compounds. 

As solvents, aromatic hydrocarbons (benzene, toluene), and chlorinated derivatives of aliphatic or aromatic hydrocarbons can be used. Reference 3 includes some technological details and the factors that influence the development of the synthesis process. 

The ratio of the chloride mixture mainly derives from the toluene/chlo-rine ratio and the contact time. Benzyl chloride is produced hy passing dry chlorine into hoiling toluene (110°C) until reaching a density of 1.283. At this density, the concentration of henzyl chloride reaches the maximum. Light can initiate the reaction. 

When the two groups in disubstituted benzenes are different, the same three isomers are possible that are possible when the substituents are the same. Compounds with two different substituents are usually named as positional derivatives of a monosubstituted (parent) compound. Above, the common (and commercial) name for methylbenzene is toluene, and the chlorinated derivatives are named as shown above. However, the same two chlorinated derivatives can also be properly named 2-chloromethylbenzene and 4-chloromethylbenzene. In this case, for naming, the parent compound is methylbenzene and it is understood that the methyl group is in the 1-position. The terms ortho- (1,2-), meta- (1,3-), and para- (1,4-) are also sometimes used for example, 2-chlorotoluene can be called ortho-c Aoioio -uene. This can be very confusing, but in the chemical industry, outside of the research labs, the common names for the parent compounds are almost always used. 

With trisubstitution by the same or different substituents, the three positional isomers shown above are possible. When the substituent groups are the same, the positional numbers are given followed by the suffix tri-. For example, if the three groups are chlorine, the first isomer above is named 1,2,3-trichlorobenzene. The compound above with different substituents is named as a derivative of the parent compound toluene (methylbenzene) where it is understood that the methyl group is in the 1-position. 

Bakke et al. (1982) have shown how montmorillonite catalyses chlorination and nitration of toluene nitration leads to 56 % para and 41 % ortho derivative compared to approximately 40 % para and 60 % ortho derivatives in the absence of the catalyst. Montmorillonite clays have an acidity comparable to nitric acid / sulphuric acid mixtures and the use of iron-exchanged material (Clayfen) gives a remarkable improvement in the para, ortho ratio in the nitration of phenols. The nitration of estrones, which is relevant in making various estrogenic drugs, can be improved in a remarkable way by using molecular engineered layer structures (MELS), while a reduction in the cost by a factor of six has been indicated. With a Clayfen type catalyst, it seems possible to manipulate the para, ortho ratio drastically for a variety of substrates and this should be useful in the manufacture of fine chemicals. In principle, such catalysts may approach biomimetic chemistry our ability to predict selectivity is very limited. 

Thus hydrochloric acid is a derivative of chlorine. About 93% of it is made by various reactions including the cracking of ethylene dichloride and tetrachloroethane, the chlorination of toluene, fluorocarbons, and methane, and the production of linear alkylbenzenes. It is also a by-product of the reaction of phosgene and amines to form isocyanates. 

When ortho chloro toluene is used instead of the para isomer, nitration will yield the 2.4 derivate (with respect to the chlorine). Fluorination of the R3 group involves an extra step after chlorination and before nitration. 

The higher homologues of toluene such as ethylbenzene are not usually halogenated selectively and mixtures are often produced (see Chapter 3). In the case of ethylbenzene itself, the major product of chlorination is the 1-substituted product (56%). Bromine is more selective and the 1-bromo derivative 7 is formed exclusively. 

Derivation (1) Decarboxylation of phthalic anhydride in the presence of catalysts (2) chlorination of toluene to yield benzotrichloride, which is hydrolyzed to benzoic acid (3) oxidation of toluene (4) from benzoin resin. 

Derivation Chlorination of toluene, until two formula weights of chlorine are absorbed, in absence of catalysts but presence of light. 

Brominations are, in most cases, carried out by methods similar to those for the preparation of chlorine derivatives. Sampey (127) gives a history of the photobromination of benzene and toluene. Davis (123) made a thorough examination of the relative rates of bromination of the olefins, concentrating particularly on ethylene. An unusual method for producing bromine compounds is by the use of bromosuccinimide or related compounds. This method is called the Wohl-Ziegler reaction and causes allylic bromination. It has been the subject of a couple of reviews (124,1 0). 

Chlorination reactions are also highly exothermic and the use of microflow systems is quite effective for conducting the reaction in a controlled manner. Various chlorination reactions including chlorination of toluene derivative to obtain benzyl chlorides, chlorination of acetic acid to obtain chloroacetic acid, and radical chlorination of alkanes using microflow systems have been reported. 

However, in the course of a recent mechanistic study of the electrophilic chlorination of toluene in the presence of a mixture of bis(4-chlorophenyl)selenide-Lewis acid as catalyst, Graham et al studied the decomposition of bis(4-chlorophenyl) (4-methylphenyl)selenonium chloride (36). They found that the ligand coupling pathway occured only in the presence of aluminum (O) chloride. Moreover, only chlorotoluene derivatives were obtained dichlorobenzene was not detected. The reductive elimination appears to be obviously mostly intramolecular. However, the important amount of o/t/io>chlorotoluene is not consistent with a single ligand coupling mechanism." ... 

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