Grignard method

Silicones and Other Heat-resisting Polymers 29.2.1 The Grignard Method... 

The Grignard method was the first route used commercially in the production of silicone intermediates. Its great advantage is its extreme flexibility since a wide range of organic groups may be attached to the silicon in this method. Because of the need to use ether or other inflammable solvents considerable production hazards arise. On economic grounds the main drawbacks of the process are the multiplicity of steps and the dependence on silicon tetrachloride, which contains only 16% Si and is thus a rather inefficient source of this element. 

The synthesis and mechanism of formation of a triazene from an arenediazonium ion and an amine with one or two aliphatic substituents (see Scheme 13-1, R = alkyl, R = H or alkyl) will be discussed in Section 13.2. Here we will briefly mention Dimroth s method (1903, 1905 a) for synthesis of wholly aliphatic triazenes (Scheme 13-6, R and R = alkyl). Dimroth obtained these by the action of Grignard reagents on alkyl azides followed by isolation via copper(i) salts. The Grignard method can also be applied for the synthesis of triazenes with an aromatic substituent by using an aryl azide. 

Ansuer The Grignard method will be best for making (27) from secondary halide (28) as it avoids elimination reactions likely with cyanide ion. Disconnection (29a) now leads back to an alcohol (30) which can be made in a similar manner as (24). 

Advanced Example In research on violet perfumes, aldehyde (33) became a key Intermediate for a new series of compounds. Dlels-Alder disconnection gives acrolein and diene (34) which can he made by the Grignard method from available enone (36),... 

First thoughts might be of a Friede1-Crafts disconnect ion using anhydride (2) which could be made from cyclohexene. An alternative is to reconnect (1) immediately to (3) and make this by standard Grignard methods. Both routes use the same disconnections. 

Chlorodialkylphosphines are important synthetic intermediates in organophosphorus chemistry. In the chemical literature there is a widespread view that the simple one-step Grignard method is not suitable for the preparation of these compounds because of dominant trisubstitution and the formation of difficultly separable mixtures.12 Although this is true for the w-alkyl compounds, the present preparation demonstrates that in the case of branched primary alkyl compounds and secondary and tertiary alkyl compounds the method can be very convenient and can give pure products. The submitters have prepared 13 chloro-diisobutylphosphine (45-50%), chlorodi-sec-butylphosphine (75-80%), chlorodi-f-butylphosphine (65-70%), and chlorodicyclo-hexylphosphine (60-65%) in analogous manner. 

Previously published methods for the synthesis of dimethylzinc, a useful alkylating agent, include the reaction of dimethylmercury with metallic zinc,1 the reaction of a zinc-copper couple with methyl iodide,2 and the Grignard method.3 The reaction of trimethylaluminum with zinc(II) halides or alkoxides can be used,4 but it is more convenient to use zinc(ll) acetate, which is very readily obtained by dehydrating the commercial dihydrate with boiling acetic anhydride or by the reaction5 ... 

Formamide and other Derivatives of Formic Acid (Grignard).—This is the Grignard method of preparing aldehydes. The same remarks apply to this reaction as to the other Grignards dealt with. The equations illustrate its course. 

The direct hydrogenation to deoxidize fatty acid esters results in hydrocarbons with one carbon atom less than the number present in the hydrocarbon chain of the original ester. The reaction can be carried out quantitatively, but it is a relatively drastic chemical operation. In the Grignard method the hydrocarbon chain of the molecule is lengthened the reactions are executed at relatively low temperatures the overall yield amounts to 70-90% of the theory. 

Samples of triphenylborane are obtained readily by thermal decomposition of trimethylammonium tetraphenylborate prepared by the method described. Preparation of triphenylborane by this method eliminates the tedious and somewhat hazardous treatment of the reactive residues produced during the formation of the triphenylborane by the Grignard method.3... 

The Grignard method is generally applicable to the preparation of ji-allyl complexes, e.g. ... 

From the turn of the century on, the principal route for linking a carbon-silicon bond in synthesizing variously substituted silanes was the classical Grignard method , first introduced by Kipping17,18 and Dilthey19. Unfortunately, this reaction was mainly limited to obtain (organo-) saturated organosilanes. 

Given a carboxylic acid, write an equation for its synthesis by hydrolysis of a nitrile (cyanide) or by the Grignard method. 

The synthesis of 18 exemplifies the Grignard method. The reagent is made1 from the alkyl halide with magnesium metal in dry ether and combined, without isolation, with the electrophile— all steps being carried out under strictly anhydrous conditions. 

From 1914, the Grignard method of synthesis completely displaced the organozinc method and was widely used674. Up to 1960, fifty publications reporting the use of this method appeared125,675. 

Bis[4-acetylphenyl] Ditellurium [Grignard Method] 1 The Grignard reagent is prepared from 4.09 g (0.0165 mol) of the 1,2-dihydroxycthane acetal of 4-acetylbromobenzene in 50 ml of tetrahydrofuran and the solution cooled to 0°. 3.15 g (0.025 mol) of powdered tellurium are added and the mixture is stirred in the flask, which is open to the atmosphere, for 10-15 h. 4 Molar aqueous hydrochloric acid is added to pH 2.5 and the ditcllurium compound is extracted with three 50 ml portions of diethyl ether. The combined extracts arc filtered, dried with sodium sulfate, the solvent is evaporated, and the residue is recryslallized from diethyl ether yield 0.36 g (9%, based on bromoacetal) m.p. 104-106°. 

Scheme 7.6 Preparation of 1,5-cy clo octadiene (1,3,5-cycloheptatriene) and 1,5-cyclooctadiene(l,3,5-cyclooctatriene) metal(O) complexes via the isopropyl Grignard method (25, 27 ...

Added importance centers on the dialkyldialkoxysilanes in view of the fact that they are satisfactory intermediates for the manufacture of silicon resins. These compounds may be made by a modification of the Grignard method without the use of ether as a solvent,58 and many of the alkyltriethoxysilanes listed in the compound index at the end of this chapter also were made this way.69 The allyltri-ethoxysilane so prepared apparently did not polymerize, but the phenylethynylsilanes prepared by the following reactions... 

The classical Grignard method of synthesis does not lend itself to the joining of alternate silicon atoms and methylene groups, because... 

The most straightforward solution to the problem of producing methyl-, ethyl-, and phenylchlorosilanes would be to adapt the classical laboratory methods of synthesis to large-scale operation. A logical choice would be the Grignard reaction, long a laboratory favorite because it is so universally applicable. For the preparation of dimethyl silicone from inethyl chloride by the Grignard method, the steps would be ... 

With this discussion as a basis, the entire process for the preparation of a silicone polymer by the Grignard method can be shown in diagrammatic form in Fig. 1. This flow sheet does not specify the type of... 

If attention at first is confined to the production of methyl silicone from the previously accepted raw materials, the chemical processes must include reduction of silica to silicon, preparation of the methyl chloride from methane or methanol, reaction of the methyl chloride with silicon, and hydrolysis of the methylchlorosilanes. If the same conventions are used as in the discussion of the,Grignard method, and the methanol process for methyl chloride is elected, the steps are ... 

It is evident that this process is simpler in its requirements than the Grignard method and involves fewer chemical operations. Since the silicon need not be chlorinated, no free chlorine is required. The hydrochloric acid produced by the hydrolysis of dimethyldichloro-silane is exactly consumed by the reaction with methanol, so that two... 

As in other preparative methods for organosilicon compounds, the direct synthesis produces a mixture of methylchlorosilanes rather than the single compound shown in equation 3. Besides dimethyl-dichlorosilane, the mixture usually contains silicon tetrachloride, tri-chlorosilane, methyltrichlorosilane, methyldichlorosilane, trimethyl-chlorosilane, and even silicon tetramethyl. Under proper conditions, dimethyldichlorosilane is the principal product. Of the other compounds, methyltrichlorosilane usually is next in abundance this substance finds use in the cross-linked methyl silicone resins, or it can be methylated further by the Grignard method to increase the yield of dimethyldichlorosilane. There is no way of recycling it in the direct process, and so supplemental operations are required for the conversion. The interconversion of this and the other minor products of the direct synthesis, involving the exchange of methyl and chlorine groups as desired, has been a special study in itself.10... 

---