Big Chemical Encyclopedia

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

Articles Figures Tables About

Alkyl halides General methods from alcohols

General methods from alcohols Triphenylphosphine-Diethyl azodicar-boxylate-Lithium halides, 332 Alkyl fluorides... [Pg.382]

Reduction of an alkyl halide, either via the Grignard reagent or directly with metal and acid, involves simply the replacement of a halogen atom by a hydrogen atom the carbon skeleton remains intact. This method has about the same applicability as the previous method, since, like alkenes, alkyl halides are generally prepared from alcohols. Where either method could be used, the hydrogenation of alkenes would probably be preferred because of its simplicity and higher yield. [Pg.91]

The most generally useful method for preparing alkyl halides is to make them from alcohols, which themselves can be obtained from carbonyl compounds, as we ll see in Sections 17.4 and 17.5. Because of the importance of the process, many different methods have been developed to transform alcohols into alkyl halides. The simplest method is to treat the alcohol with HC1, HBr, or HI. For rea-... [Pg.344]

Notable examples of general synthetic procedures in Volume 47 include the synthesis of aromatic aldehydes (from dichloro-methyl methyl ether), aliphatic aldehydes (from alkyl halides and trimethylamine oxide and by oxidation of alcohols using dimethyl sulfoxide, dicyclohexylcarbodiimide, and pyridinum trifluoro-acetate the latter method is particularly useful since the conditions are so mild), carbethoxycycloalkanones (from sodium hydride, diethyl carbonate, and the cycloalkanone), m-dialkylbenzenes (from the />-isomer by isomerization with hydrogen fluoride and boron trifluoride), and the deamination of amines (by conversion to the nitrosoamide and thermolysis to the ester). Other general methods are represented by the synthesis of 1 J-difluoroolefins (from sodium chlorodifluoroacetate, triphenyl phosphine, and an aldehyde or ketone), the nitration of aromatic rings (with ni-tronium tetrafluoroborate), the reductive methylation of aromatic nitro compounds (with formaldehyde and hydrogen), the synthesis of dialkyl ketones (from carboxylic acids and iron powder), and the preparation of 1-substituted cyclopropanols (from the condensation of a 1,3-dichloro-2-propanol derivative and ethyl-... [Pg.144]

These methods are not always applicable or convenient. A more general method used by Richard and Jencks utilizes HPLC analysis of carbocation formation in alcohol-water mixtures.22 As shown in Scheme 2 for an a-aryl ethyl cation, formation of the ether product from reaction of the carbocation with the alcohol depends on the rate constant for carbocation formation kll and the partition ratio between product formation and the back reaction to form the alcohol kROiiAii2o- This ratio may be determined from the ratio of products formed from reaction of the carbocation generated from a suitable solvolytic precursor such as an alkyl halide. [Pg.33]

The preparation and structures of siloxanediol derivatives has been reviewed29,184 but some representative examples of reactions are given below. Two general methods have been used to make metal siloxides from silanols one involves the direct reaction of a silanol with the metal derivative, usually an amide, alkoxide, halide or alkyl (to give amine, alcohol, HX or alkane byproducts respectively), while the second involves the preparation of a simple alkali metal derivative which can then be used as a siloxide transfer reagent for further synthesis. Only the direct route will be considered here. Two of the most useful siloxide transfer species, (MOPh2Si)20 (M = Li or Na), are... [Pg.717]

Isohypsic reactions of alkenes, like electrophilic additions of H2O or HX, represent a conventional pathway for the preparation of alcohols and alkyl halides from alkenes. The scope of their application was originally limited as unsymmetrical alkenes (e.g. 125) gave product mixtures composed of both Markovnikov (M) adducts and anti-Markovnikov (aM) adducts. As was already mentioned above (see Scheme 2.10), an efficient and general method for the conversion of alkenes into alcohols or ethers 126 (Scheme 2.47), with a nearly complete M selectivity, was elaborated using mercury salts as electrophiles in conjunction with the reduction of the formed adducts. It is also... [Pg.103]

Alcohols, General Methods of Preparation.—The general methods for the preparation of the alcohols, so far as they involve compounds which we have already studied, resolve into one method which has been discussed already in connection with the proof that alcohols are hydroxyl substitution products of the hydrocarbons. This is the synthesis from alkyl halides by means of water in the presence of alkalies or in excess with heat and by means of moist silver oxide, (AgOH). [Pg.92]

The Williamson reaction, discovered in 1850, is still the best general method for the preparation of unsymmetrical or symmetrical ethers.The reaction can also be carried out with aromatic R, although C-alkylation is sometimes a side reaction (see p. 515). The normal method involves treatment of the halide with alkoxide or aroxide ion prepared from an alcohol or phenol, although methylation using dimethyl carbonate has been reported. It is also possible to mix the halide and alcohol or phenol directly with CS2CO3 in acetonitrile, or with solid KOH in Me2SO. The reaction can also be carried out in a dry medium,on zeolite-or neat or in solvents using microwave irradiation. Williamson ether synthesis in ionic liquids has also been reported. The reaction is not successful for tertiary R (because of elimination), and low yields are often obtained with secondary R. Mono-ethers can be formed from diols and alkyl halides. Many other... [Pg.529]

The most important of these methods of preparation—since they are the most generally applicable—are the dehydrohalogenation of alkyl halides and the dehydration of alcohols. Both methods suffer from the disadvantage that, where the structure permits, hydrogen can be eliminated from the carbon on either side of the carbon bearing the —X or OH this frequently produces isomers. Since the isomerism usually involves only the position of the double bond, it is not important in the cases where we plan to convert the alkene into an alkane. [Pg.156]

As we shall see later, alkyl halides are generally prepared from the corresponding alcohols, and hence both these methods ultimately involve preparation from alcohols howevei, dehydrohalogenation generally leads to fewer complications and is often the preferred method despite the extra step in the sequence. ... [Pg.156]

Hydrolysis of alkyl halides is severely limited as a method of synthesizing alcohols, since alcohols are usually more available than the corresponding halides indeed, the best general preparation of halides is from alcohols. The synthesis of benzyl alcohol from toluene, however, is an example of a useful application of this method. [Pg.503]

Methods for the preparation of alkenes generally involve elimination reactions, such as dehydrohalogenation, the elimination of HX from an alkyl halide, and dehydration, the elimination of water from an alcohol. [Pg.262]

Preparation of Alkyl Halides from Olefins. There are two general methods for the synthesis of alkyl halides (1) by the interaction of an alcohol with a halogen hydride—a procedure that may reasonably be discussed under esterification or halogenation and, also, under the Friedel-Crafts synthesis when a metal halide is used to catalyze the reactions— and (2) by the addition of a halogen hydride to an unsaturated hydrocarbon. This reaction may be catalyzed by metal halides and by sulfuric acid. In the latter instance, the ethylsulfuric acid first formed is converted to the halide by gaseous chlorine or chlorine liberated in situ by action of sulfuric acid on a halide. [Pg.243]

General Methods of Preparing Alcohols.—It has already been stated that an alcohol can be prepared by replacing a halogen atom in alkyl halides by a hydroxyl group. This replacement can be effected by treating the halide with water or a metallic hydroxide. The preparation of methyl alcohol from methyl iodide is typical —... [Pg.99]

A general method, used very often practically, for the preparation of olefins consists in the action of an alcoholic solution of potassium hydroxide on an alkyl halide. This reaction is analogous to the production of ammonia from ammonium chloride and an aqueous solution of an alkali. The equations for the latter are generally given as the following ... [Pg.139]

Phosphonium ylides (alkyhdene phosphoranes) can be prepared by a number of methods, but in practice they are usually obtained by action of a base on (alkyl)triphenylphosphonium salts, which are themselves readily available from an alkyl halide and triphenylphosphine. The phosphonium salt can usually be isolated and crystallized, but the phosphonium ylide is generally prepared in solution and used without isolation. Formation of the phosphonium ylide is reversible, and the reaction conditions and the strength of the base required depend entirely on the nature of the ylide. A common procedure is to add a stoichiometric amount of a solution of n-butyllithium to a solution or suspension of the phosphonium salt in ether or THF, followed, after an appropriate interval, by the carbonyl compound. Other bases, such as sodium hydride or sodium or potassium alkoxides, in solution in the corresponding alcohol or in dimethylformamide, are used commonly. [Pg.134]


See other pages where Alkyl halides General methods from alcohols is mentioned: [Pg.477]    [Pg.216]    [Pg.386]    [Pg.388]    [Pg.314]    [Pg.82]    [Pg.580]    [Pg.1301]    [Pg.232]    [Pg.243]    [Pg.425]    [Pg.313]    [Pg.100]    [Pg.846]    [Pg.1097]    [Pg.166]    [Pg.365]    [Pg.1097]   


SEARCH



Alcohol, generally

Alcohols alkylated

Alcohols alkylation

Alcohols, general

Alkyl alcohols

Alkyl halides from alcohols

Alkylation Method

From alkyl halides

Halides from alcohols

© 2024 chempedia.info