Kharasch method

For a method of preparing organoboranes from RMgX and BF3, where the RMgX is present only in situ, see Brown, H.C. Racherla, U.S. Tetrahedron Lett., 1985, 26, 4311. For reviews as applied to Si, B, and P, see Wakefield, Ref. 291, p. 149 Kharasch, M.S. Reinmuth, O. Grignard Reactions of Nonmetallic Substances Prentice-Hall Englewood Cliffs, NJ, 1954, p. 1306. 

Undoubtedly, the most notable feature of these new dendrimeric organometallic molecules is their ability to act successfully as effective homogeneous catalysts for the Kharasch addition reaction of polyhalogenoalkanes to olefinic C=C double bonds. Indeed, they show catalytic activity and clean regiospecific formation of 1 1 addition products in a similar way to that observed in the mononuclear compounds. Likewise, the nanoscopic size of these first examples of soluble dendritic catalysts allows the separation of such macromolecules from the solution of the products by ultrafiltration methods. 

Kharasch Sosnovsky J. Org. Chem. 19S8, 23, 1322 Ledaal Acta Chem. Scand. 1967, 21, 1656. For another method, sec Sanderson Zciler Synthesis 1975, 125. 

An expln can be produced on contact of DMSO with 70% perchloric acid as was reported by Kharasch (Ref 3) Vacuum distn of DMSO over anhyd Mg perchlorate by the method described in Ref 4, performed by a graduate student in. a lab of Washington... 

The addition of a single-bonded reagent across a multiple bond is one of the fundamental reactions of organic radicals. The basic principles of this reaction were first advanced by Kharasch in pioneering studies on the mechanism of the peroxide-initiated anti-Maikovnikov addition of hydrogen bromide to alkenes.1 In the atom transfer method, the generation and removal of radicals are coupled and occur in the key atom transfer step. Compared to other methods, the atom transfer method provides unique options for synthetic reactions. But there are also important limitations. Recently, there has been a renewed interest in the application of the characteristics of atom transfer reactions in synthesis and new developments have been reviewed.5,161... 

Berzelius1 prepared platinum(II) chloride by evaporation of a solution of hexachloroplatinic(IV) acid and heating of the residue to about 300 to 350° with constant stirring. This method has been more recently modified by Kharasch and Ashford.2 Nilson3 obtained a more pure product by evaporation of a solution of tetrachloroplatinic(II) acid. The preparation of pure platinum (II) chloride from readily obtainable hexachloroplatinic(IV) acid 6-hydrate is given here. This is an adaptation of the method of Wohler and Streicher.4... 

The commercial production of mercury fungicides from organolead compounds is based on patents by Kharasch 184,185). The mercury compounds are used in the disinfection of seeds and grains. Typical compounds are ethylmercuric chloride, ethylmercuric sulfate, ethyl-mercuric phosphate, phenylmercuric acetate, and compounds derived from substituted phenols and ureas. The manufacture of these compounds was reviewed by Whelen in 1957 310>. The alkylation reaction is a general reaction, and a number of additional patents has been issued on methods similar to Whelen s. A representative equation is ... 

The copper-catalyzed 1,4-addition of Grignard reagents to enones has been described by Kharasch in 1941, that is, one decade before the discovery of Gilman cuprates (1952) and more than two decades before the first use of organocuprates in conjugate addition reactions. Consequently, numerous variations and applications of the method have been reported over the years.3 5,7 7a 23 Not surprisingly, several of the advances made in the last decade with... 

The procedure for the preparation of the platinum compounds is an extension of the method described by Kharasch and Ashford.5 A glacial acetic acid solution of chloroplatinic acid is mixed with the appropriate olefin, and in the ensuing reaction the platinum is reduced from the 4+ oxidation state to the 2 + state. The overall stoichiometry of these reactions is not known however, the reduction of the platinum is1 accompanied by the partial oxidation of the olefin. 

M. S. Kharasch et al., Scicnccy 102, 128 (1945), were the first to demonstrate a 1 1 addition of either CCI4 or CUCI3 across the double bond of octene-1 to produce CCI3—CHCl—(CH.2)6—H and CCh—(CH2)t—H, respectively. This has bec ome an important method of synthesis. The reaction is called telemerization. 

Following the pioneer work of Kharasch [60], methods involving radical transfer of halides have been developed. The atom transfer method has emerged in the 1980s as one of the best method for conducting intra- and intermolecular radical additions to olefins [61]. This approach is particularly appealing from an atom economy point of view since all atoms remains in the final product. The non-reductive nature of these reactions is also particularly important for the preparation of functionalized molecules. Halides transfers and more particularly iodine atom transfers have found nice applications for cyclizations, annula-tions and cascade reactions [62]. These reactions are based on exothermic radical steps, such as the addition of an alkyl radical to an olefin, followed by an... 

Tris(dimethylamino)phosphine (tdp) is prepared by the method of Burg and Slota. The benzonitrile complex, irans-[PdCl2(PhCN)2], is prepared by Kharasch s method. The benzene is dried over Linde 4-A molecular sieve. 

In 1938 Kharasch and co-workers described a method generally applicable for preparing mono-olefin palladium complexes (14 ). Palladium (II) chloride reacted with warm benzonitrile to form the complex bis(benzonitrile)-palladium chloride, and the latter reacted directly with olefins such as ethylene, styrene, cyclohexene, etc., as follows ... 

Many investigators have attempted to isolate mercury derivatives from aceto-acetie ester, but the results have been so varied that no reliance can be placed on any of the early work on this compound. Kharasch and Staveley, however, have obtained definite results by heating mercury salts of substituted acetic acids in vacuo, e.g, di-method and diethyl aceto-acetic acids when dried and heated in vacuo at 90 C. evolve carbon dioxide, and the mercury becomes bound to the carbon atoms which were formerly attached to the carboxyl groups —... 

Chlorination of alkanes. Kharasch developed a method for the low-temperature radical chlorination of alkanes utilizing sulfuryl chloride catalyzed by dibenzoyl peroxide. 

In its simplest form, the method proposed by M. S. Kharasch (1929) is virtually the same as that just described. The molar heat of combustion of a liquid compound at constant pressure is equal to — 26.05x kcal., where X is the number of valence electrons of carbon not shared with oxygen in the original substance, but which are shared with oxygen, i.e., in carbon dioxide, when combustion is complete. In general, x is equal to twice the number n of oxygen atoms utilized in the combustion of a molecule, so that this rule is equivalent to stating that the heat of combustion is — 52. In kcal. per mole. However, Kharasch has realized the necessity for including allowances for various types of structure in the compound, and by the use of these correction factors results have been obtained which are within one per cent, or less, of the experimental heats of combustion. 

It is probable that tetrachloro(diethyIene)diplatinum(II) was first prepared by Zeise by decomposition of trichloro-(ethylene)platinic(II) acid.1 Boiling hexachloroplatinic-(IV) acid with chloroform also gave the compound.2 However, it was first obtained in sufficient quantity for investigation by Anderson,3 who boiled an ethanolic solution of sodium hexachloroplatinate(IV) 6-hydrate until reduction to platinum(II) was complete. This procedure is tedious, and the yields are affected markedly by impurities in the platinum salt and by the presence of other platinum metals.4 Optimum yields of 75% are obtained only after much experience. The general method of Kharasch and Ashford,5 involving adding an olefin to a suspension of platinum(IV) chloride in warm benzene or glacial acetic... 

There are numerous publications on the improvements to the Kharasch reaction. The primary method for improvement was the introduction of more sophisticated initiators (instead of peroxides [22-26, 37]). It was shown that various Red-Ox type initiators, like metal salts in different oxidation states (Cu", Cu ", Fe ", etc.), salts with organic acids (Co acetoacetate, Mn stearate), and a metal carbonyl - Fe(CO)5 give adducts with practical yields [38, 39] and allow to carry the reaction at near room temperatures (Fig. 30). 

The tributyltin hydride-mediated carbon-carbon bond formation via radical addition and cyclization of alkyl halides with alkenes has often been a choice for construction of various organic molecules [1], However, the requirement for high-temperature initiators or photo initiation and the difficulties associated with purification of the products from tributyltin halides tend to limit the widespread use of these methods, despite the efforts to make the methods easier [Ic, 2], Recently, nickel-mediated radical additions and cyclizations have been introduced as promising alternatives to the tributyltin hydride methods. These are the nickel powder-acetic acid method for cyclization of haloamides to y-lactams, y -lactams and in-dolones, the borohydride exchange resin-nickel boride method for radical addition, nickel-catalyzed electroreductive cyclization and nickel-catalyzed Kharasch addition of polyhalo compounds. 

Diethylstilbesterol may be synthesized by two different methods. First, from anisaldehyde (Dodds and Lawson, 1939) and secondly, from anethole (Kharasch et al. 1943). The latter shall be diseussed here. 

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