Alkyl chlorides, formation from alcohols

Formation of Ethers. Very high ether yields can be obtained from alcohols and phenols with dialkyl sulfates in CH2CI2 and concentrated NaOH—tetrabutylammonium chloride at room temperature or slightly elevated temperature within 1—5 h (18). Using excess aqueous caustic—N(C4H2)4HS04, unsymmetrical aUphatic ethers can be prepared with alkyl chlorides at 25—70°C in 3—4 h (19) (see Ethers). 

Although detailed mechanisms have not been established, the first step is thought to be formation of an unstable mixed anhydride, which then extrudes S02 and collapses with attack of chloride at the carbonyl carbon. A similar mechanism occurs in the formation of alkyl chlorides from alcohols and thionyl chloride (Section 15-5A) ... 

Reaction XLIII. (a) Formation of Esters by the action of Acid Anhydrides or of Acid Chlorides on an Alcohol in the presence of Magnesium Alkyl Halide (Grignard). (B., 39, 1738.)—This application of the Grig-nard reaction to the preparation of esters is of theoretical rather than practical interest as illustrating the wide applicability of this many-sided reaction. The steps in the synthesis will be clear from the examples given they are somewhat different from the usual phases of a Grignard reaction. 

The formation of alkyl bromides is more ready than that of the alkyl chlorides. Hence secondary as well as tertiary bromides can be obtained directly from the corresponding alcohols by heating with constant boiling hydrobromic acid (e.g. Expt 5.53), although in the case of primary alcohols the presence of sulphuric acid results, as a rule, in a more rapid reaction and in improved yields. 

Alcohols and aldehydes are also suitable materials for the creation of an alkyl amine. In addition to the aforementioned formation of alkyl chloride as an intermediate, alcohols can be directly converted to amines under hydrogenation conditions in the presence of ammonia while aldehydes are prereacted to form imine followed by hydrogenation [13]. Selectivity of the primary amine with these techniques is difficult and this process is more typically utilized for the preparation of tertiary amines where the reaction can be driven to completion. In certain cases, alcohols and aldehydes provide structural elements which are not attainable from natural sources. An example is the formation of a hydrogenated tallow 2-ethyl hexyl amine. The amine is prepared as shown below in eqn 6.1.8 using a hydrogenated tallow amine reacted with 2-ethyl hexanal [14, 15] ... 

A related reaction is the formation of alkyl chlorosulfonates from alcohols and sulfuryl chloride. ... 

Whether an alcohol is primary, secondary, or tertiary is shown by the Lucas test, which is based upon the difference in reactivity of the three classes toward hydrogen halides (Sec. 16.4). Alcohols (of not more than six carbons) are soluble in the Lucas reagent, a mixture of concentrated hydrochloric acid and zinc chloride. (Why are they more soluble in this than in water ) The corresponding alkyl chlorides are insoluble. Formation of a chloride from an alcohol is indicated by the cloudiness that appears when the chloride separates from the solution hence, the time required for cloudiness to appear is a measure of the reactivity of the alcohol. 

In the case of hydrobromic and hydriodic acids and such olefins as isobutylene and tri methyl ethylene, the rate of alcohol formation may become such that it approaches the rate of hydrolysis of the corresponding alkyl halides, thus supporting the theory that halides are the necessary intermediate product.04 The greater activity of the hydrobromic and hydriodic acids compared with hydrochloric acid toward ethylene is shown by the experiments of Swann, Snow and Keyes.00 At 800 pounds per square inch pressure and a temperature of 150° C. no alkyl chlorides were detected when hydrochloric acid of from 5 to 25 per cent concentration was used. On the other hand, considerable yields of alkyl iodides were obtained under the same conditions when hydriodic acid was used, and alkyl bromides formed in the presence of 40 per cent concentration hydrobromic acid. Alcohol yields were very small. When using propene at 600 to 800 pounds per square inch pressure at 135° C. in the presence of 5 per cent hydrochloric acid solutions and solutions of silver nitrate, yields of alcohol several times that obtained from ethylene were found. The yields were still very low, however, even with times of reaction as long as one hour. 

Chlorosilanes are also converted to siloxanes by reactions not involving hydrolysis. Most are highly exothermic, and appropriate measures for heat dissipation are recommended for safety. Thus chlorosilanes can be converted to siloxanes by reaction with DMSO or with NajCOj or ZnO in suitable solvents such as ethyl acetate or dioxane. Siloxanes can also be obtained by the reaction of alcohols with chlorosilanes, but this is really a kind of hydrolysis in which the water is generated in situ as a by-product of the formation of alkyl chloride from the alcohol and HCl. Siloxanes can of course be prepared from the reaction of HjO with many other kinds of hydrolyzable silanes (e.g., sulfato, iodo, bromo, fluoro, alkoxy, aryloxy, acyloxy, amino, amido, ketoximo) but such intermediates are themselves derived from chlorosilane precursors. Acetoxysilanes undergo thermolysis to yield siloxane bonds. 

Alkyl chlorides.Alcohols react with hydrogen chloride in HMPT at 50-85° to form alkyl chlorides in 65-90% yield. The reaction of primary alcohols is rapid (30 min.) longer reaction times are required for secondary and tertiary alcohols (about 1 hr.). Neopentyl alcohol reacts without formation of rearranged products. Racemic product was obtained from 2-octanol. 

Cations can be formed from alcohols, and they add to aromatic rings in the usual manner. Sulfuric acid is a common catalyst for alcohols, forming an alkyl sulfate that then reacts with the aromatic substrate. 120 Alcohols are more reactive than halides, although large quantities of the Lewis acid are usually required for Friedel-Crafts reactions.I2l Alcohols form a complex with aluminum chlorides [R(H)0— A1C13], and a complicating side reaction is loss of HCl and formation of an alkyl chloride.122 a full equivalent of the Lewis acid... 

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