Dialkyl halide

Many other reactions have been reported for the synthesis of polyesters, such as reactions between dicarboxylic acid salts and dialkyl halides, reactions between... 

Certain aluminum alkyls and aluminum dialkyl halides in the presence of proton- or carbonium-donating cocatalysts act as effective polymerization catalysts. 

Hydrolysis of the API melphalan is an example involving nitrogen group assistance of solvolysis of a dialkyl halide to form the dialkyl alcohol (Fig. 90) (130). 

L = trans to R). The initial dialkyl halide can undergo alkyl halide interchange with the Au(I) alkyl to give trialkylAu(III) complexes, which can be isolated ... 

The following ammonia and amine compounds of tin dialkyl halides have recently been described tin dimethyl dichloride dianiline, McaSn Clg.SPhNHg the diquinoline salt forms white crystals, M.pt. 40 to C, unstable in moist air, the dibromide melting at 80° to 115° C. Tin diethyl dichloride and dibromide both form dianiline, and the latter a monoaniline compound. Tin dipropyl dibroxnidc yields a dianiline derivative. 

In its covalent compounds thallium shows no reluctance to utilizing the two 6s electrons for bond formation. Indeed monoalkyl derivatives Tl(Alk) in which the valence group would be (2, 2) are not known, whereas trialkyls (valence group 6) are known and the most stable alkyl derivatives are the dialkyl halides such as [T1(CH3)2]I. These are ionic compounds-[T1(CH3)2] OH being a strong base—and in the Tl(Alk)2 ions the thallium atom has the same outer electronic structure as mercury in CH3-Hg-CH3, viz. (4). Accordingly the (CH3-T1-CH3) ion is linear, as shown by the determination of the crystal structure of Tl(CH3)2l. In molecules such as Tl(Alk)2A, where A represents a molecule of a /3-diketone, T1 apparently has the valence group (8). 

Highly syndiotactic polypropylene was prepared by Natta and co-Workers with homogeneous catalysts formed from VCU or from vanadium triacetylacetonate, aluminum dialkyl halide, and anisole at -48 to -7 8 °C. No isotactic fractions formed. This led to the development of many effective soluble catalysts. The catalyst components and the conditions for their preparation are quite important in maintaining control over syndiotactic placement. For the most effective soluble catalyst the ratio of AIR2X to the vanadium compound must be maintained between 3 and 10. The organic portion of the organoaluminum compound can be either methyl, ethyl, isobutyl, neopentyl, phenyl, or methylstyryl. " In addition to VCI4 and to vanadium triacetylacetonate, various other vanadates can be used, like [ VO(OR)/ l3 c], where x = 1,2, or 3 The exact nature of the vanadium... 

Highly syndiotactic polypropylene was prepared by Natta et al. [38] with homogeneous catalysts formed from VCI4 or fi om vanadium tri-acetylacetonate, aluminum dialkyl halide, and anisole at —48 to 78°C. 

Esters are alkylated in the presence of strong bases in aprotic solvents. A common combination is LDA in tetrabydrofuran at low temperatures. Equimolar amounts of base are sufficient and only the mono-carbanion Js formed. After addition of one mole of alkyl halide the products form rapidly, and no dialkylation, which is a problem in the presence of excess base, is possible. Addition of one more mole of LDA and of another alkyl halide leads to asymmetric dialkylation of one or-carbon atom in high yield (R.J. Cregge, 1973). 

Dialkyl arylphosphonates and alkenylphosphonates are prepared by the coupling of halides or triflates with the dialkyl phosphonate 783[64l-643]. 

The cleavage of dialkyl ethers by hydrogen halides was discussed in Section 16 8 where It was noted that the same pair of alkyl halides results irrespective of the order in which the carbon-oxygen bonds of the ether are broken... 

Attack by the halide nucleophile at the sp hybridized carbon of the alkyl group is anal ogous to what takes place in the cleavage of dialkyl ethers Attack at the sp hybridized carbon of the aromatic nng is much slower Indeed nucleophilic aromatic substitution does not occur at all under these conditions... 

IV-Methylated pyridazinones can be obtained from 3,6-dialkoxypyridazines by treatment with alkyl halides or dialkyl sulfates. Methyl iodide and dimethyl sulfate are most frequently used. According to the proposed mechanism, an intermediate quaternary pyridazinium salt is formed, followed by elimination of a group R from the alkoxy group. At higher temperature, l,2-dimethylpyridazine-3,6(l//,2//)-dione is formed with dimethyl sulfate. 

One of the advantages of the enamine alkylation reaction over direct alkylation of the ketone under the influenee of strong base is that the major product is the monoalkylated derivative 29,32). When dialkylation is observed, it occurs at the least substituted carbon in contrast to alkylation with base, where the a-disubstituted product is formed. Dialkylation becomes the predominant reaction when a strong organic base is added and an excess of alkyl halide is used (29). Thus 1-N-pyrrolidino-l-cyclo-hexene (28) on treatment with two moles of allyl bromide in the presence of ethyl dicyclohexylamine (a strong organic base which is not alkylated under the reaction conditions) gave a 95 % yield of 2,6-diallylcyclohexanone (29). 

In the alkylation of enolate anions, a mixture of mono- and polyalky lation produets is usually obtained, and when enolization of a di-a-methylene ketone is possible toward both sides, a mixture of di-a- and a,a -dialkylation products ean be expeeted. Thus the enamine alkylation sequenee beeomes partieularly attractive when eontrolled monoalkylation is imperative beeause of difficulties in separation of a mixture of alkylation produets. One of its first synthetie applications was in the reaetions of /8-tetralones with alkyl halides. Yields in exeess of 80% were usually found 238-243) in these reaetions, which make valuable intermediates for steroid and diterpene syntheses more aecessible. 

A fundamental problem in the alkylation of enamines, which is inherent in the bidentate system, is the competition between the desired carbon alkylation and attack at the nitrogen. With unactivated alkyl halides (3,267), this becomes especially serious with the enamines derived fromcycloheptan-one, cyclooctanone, cyclononanone, and enamines derived from aldehydes. Increasing amounts of carbon alkylation are found with the more reactive allyl and benzyl halides (268-273). However, with allyl halides one also observes increasing amounts of dialkylation of enamines. 

It was observed already by BougaulU that the reaction of 6-benzyl-3,5-dioxo-2,3,4,5-tetrahydro-l,2,4-triazines with alkyl halides in an alkaline solution yields a mixture of the 4-mono- and 2,4-dialkyl derivatives. This mixture of alkylation products can be readily sepa-... 

The alkylation of 6-azauracil will be treated later. The first, but not exactly identified dimethyl derivative was prepared by Grundmann." The course of alkylation was studied in greater detail by Gut et al. These authors found that in aqueous alkaline solution and on using alkyl halides or dialkyl sulfates, the main alkylation product is the 1,3-dialkyl derivative (64). Since, however, the alkylation is to some... 

The rate of the alkylation reaction depends on the enolate concentration, since it proceeds by a SN2-mechanism. If the concentration of the enolate is low, various competitive side-reactions may take place. As expected, among those are E2-eliminations by reaction of the alkyl halide 2 with base. A second alkylation may take place with mono-alkylated product already formed, to yield a -alkylated malonic ester however such a reaction is generally slower than the alkylation of unsubstituted starting material by a factor of about 10. The monoalkylation is in most cases easy to control. Dialkylated malonic esters with different alkyl substituents—e.g. ethyl and isopropyl—can be prepared by a step by step reaction sequence ... 

As alkylating agents may for example be used alkyl halides, dialkyl sulfates, alkyl sulfonates and epoxides. Aryl halides and vinylic halides do not react. 

As alkylating agent an alkyl halide, alkyl tosylate or dialkyl sulfate is used in most cases the latter type of reagent is often used in the preparation of methyl and ethyl ethers by employing dimethyl sulfate and diethyl sulfate respectively. Dimethyl sulfate is an excellent methylating agent, but is acutely toxic as well as carcinogenic." ... 

Certain of the monoalkylated ethyl phenylacetates have been further alkylated with alkyl and aralkyl halides to produce the corresponding disuhstituted phenylacetic esters.4 Ethyl 2-phenyl-propanoate has been alkylated by methyl iodide to give pure ethyl 2-methyl-2-pheny]propanoate in 81% yield. Similarly, the alkylations of ethyl 2-phenylhexanoate with methyl iodide, M-butyl bromide, and benzyl chloride gave the corresponding pure dialkylated products in 73%, 92%, and 72% yields, respectively. 

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-... 

The most valuable and comprehensive kinetic studies of alkylation have been carried out by Brown et al. The first of these studies concerned benzylation of aromatics with 3,4-dichloro- and 4-nitro-benzyl chlorides (these being chosen to give convenient reaction rates) with catalysis by aluminium chloride in nitrobenzene solvent340. Reactions were complicated by dialkylation which was especially troublesome at low aromatic concentrations, but it proved possible to obtain approximately third-order kinetics, the process being first-order in halide and catalyst and roughly first-order in aromatic this is shown by the data relating to alkylation of benzene given in Table 77, where the first-order rate coefficients k1 are calculated with respect to the concentration of alkyl chloride and the second-order coefficients k2 are calculated with respect to the products of the... 

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