Industrial preparation

The reaction shown is important in the industrial preparation of dichlorodimethylsilane for eventual conversion to silicone polymers... 

Although alkenes typically react with chlorine and bromine by addition at room tern perature and below (Section 6 14) substitution becomes competitive at higher tempera tures especially when the concentration of the halogen is low When substitution does occur It IS highly selective for the allylic position This forms the basis of an industrial preparation of allyl chloride... 

Alkenyl halides such as vinyl chloride (H2C=CHC1) do not form carbocations on treatment with aluminum chloride and so cannot be used m Friedel-Crafts reactions Thus the industrial preparation of styrene from benzene and ethylene does not involve vinyl chloride but proceeds by way of ethylbenzene... 

Dehydrogenation of alkylbenzenes although useful m the industrial preparation of styrene is not a general procedure and is not well suited to the laboratory prepara tion of alkenylbenzenes In such cases an alkylbenzene is subjected to benzylic bromi nation (Section 11 12) and the resulting benzylic bromide is treated with base to effect dehydrohalogenation... 

Not so for synthesis in the chemical industry where a compound must be prepared not only on a large scale but at low cost There is a pronounced bias toward reactants and reagents that are both abundant and inexpensive The oxidizing agent of choice for example in the chemical industry is O2 and extensive research has been devoted to develop mg catalysts for preparing various compounds by air oxidation of readily available starting materials To illustrate air and ethylene are the reactants for the industrial preparation of both acetaldehyde and ethylene oxide Which of the two products is ob tamed depends on the catalyst employed... 

During this period of intense synthetic research, a search for inexpensive raw materials for the partial synthesis of steroids was initiated. Abundant quantities of the sapogenin diosgenin [512-04-9] were isolated from plant sources and used for the industrial preparation of steroids (9). 

Key intermediates in the industrial preparation of both nicotinamide and nicotinic acid are alkyl pyridines (Fig. 1). 2-Meth5l-5-ethylpyridine (6) is prepared in ahquid-phase process from acetaldehyde. Also, a synthesis starting from ethylene has been reported. Alternatively, 3-methylpyridine (7) can be used as starting material for the synthesis of nicotinamide and nicotinic acid and it is derived industrially from acetaldehyde, formaldehyde (qv), and ammonia. Pyridine is the principal product from this route and 3-methylpyridine is obtained as a by-product. Despite this and largely due to the large amount of pyridine produced by this technology, the majority of the 3-methylpyridine feedstock is prepared in this fashion. 

Dinitroanthraquinones are industrially prepared by nitration of anthraquiaone in mixed nitric—sulfuric acid at 0—50°C. The reaction mixture is then heated to a temperature slightly higher than the nitration reaction temperature to enrich the content of 1,5-dinitroanthraquinone in soHd phase, and then cooled and filtered to obtain the 1,5-dinitroanthraquinone wet cake. Mother Hquor is concentrated by distillation of nitric acid and crystallised 1,8-isomer is separated. The filtrate is again distilled, and precipitated ( -isomers are filtered off and filtrate is recycled to the nitration step (72—74). 

The low molar ratio of the final UF-resin is adjusted by the addition of the so-called second urea, which might also be added in several steps [16-18]. Particular care and know-how are needed during this acid condensation step in order to produce resins of good performance, especially at the very low molar ratios usually in use today in the production of particleboard and MDF. This last reaction step generally also includes the vacuum distillation of the resin solution to the usual 63-66% solid content syrup in which form the resin is delivered. The distillation is performed in the manufacturing reactor itself or in a thin layer evaporator. Industrial preparation procedures are usually proprietary and are described in the literature in only a few cases [17-19]. 

Dehydrogenation (Section 5.1) Elimination in which H2 is lost from adjacent atoms. The term is most commonly encountered in the industrial preparation of ethylene from ethane, propene from propane, 1,3-butadiene from butane, and styrene from ethylbenzene. 

This reaction is catalysed by traces of heavy metal ions such as Cu and the purpose of the gelatin is to suppress reaction (5) by sequestering the metal ions it is probable that gelatin also assists the hydrazine-forming reactions between ammonia and chloramine in a way that is not fully understood. The industrial preparation and uses of N2H4 are summarized in the Panel. 

The reaction is convenient for both laboratory scale and industrial preparations. Another large-scale process is the reaction of CI2 gas on moist Na2C03 in a tower or rotary tube reactor ... 

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