Alkyl halides bases used

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). 

Thomson11 jW Click Organic Interactive to use a web-based palette to draw structures for alkyl halides, based on their IUPAC names. 

TPP)Rh(L)J+C1 in the presence of an alkyl halide leads to a given (P)Rh(R) or (P)Rh(RX) complex. The yield was nearly quantitative (>80X) in most cases based on the rhodium porphyrin starting species. However, it should be noted that excess alkyl halide was used in Equation 3 in order to suppress the competing dimerization reaction shown in Equation 1. The ultimate (P)Rh(R) products generated by electrosynthesis were also characterized by H l MR, which demonstrated the formation of only one porphyrin product(lA). No reaction is observed between (P)Rh and aryl halides but this is expected from chemical reactivity studles(10,15). Table I also presents electronic absorption spectra and the reduction and oxidation potentials of the electrogenerated (P)Rh(R) complexes. 

This reaction works best with primary alkyl halides. When secondary or tertiary alkyl halides are used, the alkynide reacts like a base and this results in elimination of hydrogen halide from the alkyl halide to produce an alkene ... 

N-Alkylation of 1,2,3-triazoles and benzotriazoles is readily achieved using (1) alkyl halides, dialkyl sulfates, diazoalkanes, and jS-tosylates or (2) the Mannich reaction. When alkyl halides are used, sodium alkoxide, sodium hydride, or sodium hydroxide is usually employed as the base. The N-alkylation of benzotriazole with alkyl halides proceeds efficiently using powdered NaOH as the base in DMF. The highest yields (80100%) of the alkylated benzotriazoles are obtained when a fourfold excess of NaOFl is employed. A-Alkylbenzotriazoles have been prepared from benzotriazole and alkyl halides using phase-transfer catalysts, e.g., KOFI, benzene, tetrabutyl-ammonium salts or KOH, benzene, polyethylene glycol. 

Control of the degree of alkylation of an amino acid is difficult. Alkylation can lead to /V-mono- and di-alkyl derivatives, or betaines RIN+—(CR R2—) C( >2, when an alkyl halide is used. Many practical devices can be employed to get the mono-alkylated compound. Schiff-base formation with an aldehyde, followed by reduction, is a standard route. 

The preparation of thiols involves nucleophilic substitution of the Sn2 type on alkyl halides and uses the reagent thiourea as the source of sulfur. Reaction of the alkyl halide with thiourea gives a compound known as an isothiouronium salt in the first step. Hydrolysis of the isothiouronium salt in base gives the desired thiol (along with urea) ... 

Ren and Wu showed that alcohols can be converted to alkyl halides by using 1,3-dialkylimidazolium halide-based ionic liquids as both solvent and nucleophile in... 

A difficulty in the synthesis of the phosphorylide in the Wittig reaction is to add an equimolar amount of base to the alkyl halide. The use of epichlorohydrine, which forms one equivalent of base in situ by the reaction with iodide ions, obtained from the reaction of a C-labeled alkyl iodide with triphenyl phosphine is one method to overcome the problem. Some examples of useful precursors prepared from [ C] methyl iodide are shown in O Fig. 41.7. 

One of the most popular approaches to the laboratory scale synthesis of ethers is the addition of alkoxides and phenoxides to a suitable substrate such as an alkyl bromide. This reaction is known as the Williamson ether synthesis. For primary substrates, this approach tended to work quite well, and a host of ethers have been prepared using this method. The chemistry is less straightforward when secondary or tertiary alkyl halides were used due to competing elimination processes. As a representative example, the successful synthesis of an alkyl aryl ether is shown in Example 2.2 [14]. The reaction was carried out in acetone using allyl bromide and a functionalized phenol as the substrates and potassium carbonate as the base. While many bases have been used in Williamson ether syntheses, a mild base was critical for this work since it was needed to deprotonate the phenol without deprotonating the alkyne. This was critical for the success of the chemistry as the alkyne was needed for later steps in the reaction. In related work, potassium carbonate promoted the synthesis of photo-activatable fluorescein derivatives through a Williamson ether synthesis (Scheme 2.11) [15]. It also promoted the synthesis of a morphine precursor as well (Example 2.3) [16]. 

With simple unbranched alkyl halides, the use of alcoholic bases gives the SaytzefT olefln. Steric effects on the j3-position usually increases Hofmann elimination. 

NaOCHjCHa. White solid (Na in EtOH). Decomposed by water, gives ethers with alkyl halides reacts with esters. Used in organic syntheses particularly as a base to remove protons adjacent to carbonyl or sulphonyl groups to give resonance-stabilized anions. 

A wide class of aiyl-based quaternary surfactants derives from heterocycles such as pyridine and quinoline. The Aralkyl pyridinium halides are easily synthesized from alkyl halides, and the paraquat family, based upon the 4, 4 -bipyridine species, provides many interesting surface active species widely studied in electron donor-acceptor processes. Cationic surfactants are not particularly useful as cleansing agents, but they play a widespread role as charge control (antistatic) agents in detergency and in many coating and thin film related products. 

Alkyl halides are such useful starting materials for preparing other functional group types that chemists have developed several different methods for converting alcohols to alkyl halides Two methods based on the inorganic reagents thionyl chloride and phosphorus tnbromide bear special mention... 

Similarly sodium methoxide (NaOCHj) is a suitable base and is used m methyl alco hoi Potassium hydroxide m ethyl alcohol is another base-solvent combination often employed m the dehydrohalogenation of alkyl halides Potassium tert butoxide [K0C(CH3)3] is the preferred base when the alkyl halide is primary it is used m either tert butyl alcohol or dimethyl sulfoxide as solvent... 

Substitution can take place by the S l or the 8 2 mechanism elimination by El or E2 How can we predict whether substitution or elimination will be the principal reac tion observed with a particular combination of reactants The two most important fac tors are the structure of the alkyl halide and the basicity of the anion It is useful to approach the question from the premise that the characteristic reaction of alkyl halides with Lewis bases is elimination and that substitution predominates only under certain special circumstances In a typical reaction a typical secondary alkyl halide such as iso propyl bromide reacts with a typical Lewis base such as sodium ethoxide mainly by elimination... 

Section 8 13 When nucleophilic substitution is used for synthesis the competition between substitution and elimination must be favorable However the normal reaction of a secondary alkyl halide with a base as strong or stronger than hydroxide is elimination (E2) Substitution by the Sn2 mechanism predominates only when the base is weaker than hydroxide or the alkyl halide is primary Elimination predominates when tertiary alkyl halides react with any anion... 

The acidity of acetylene and terminal alkynes permits them to be converted to their conjugate bases on treatment with sodium amide These anions are good nucleophiles and react with methyl and primary alkyl halides to form carbon-carbon bonds Secondary and tertiary alkyl halides cannot be used because they yield only elimination products under these conditions... 

Alkanethiolate ions (RS ) are weaker bases than alkoxide ions (RO ) and undergo synthetically useful 8 2 reactions even with secondary alkyl halides... 

In practice this reaction is difficult to carry out with simple aldehydes and ketones because aldol condensation competes with alkylation Furthermore it is not always possi ble to limit the reaction to the introduction of a single alkyl group The most successful alkylation procedures use p diketones as starting materials Because they are relatively acidic p diketones can be converted quantitatively to their enolate ions by weak bases and do not self condense Ideally the alkyl halide should be a methyl or primary alkyl halide... 

Polymers containing 90-98% of a c 5-1,4-structure can be produced using Ziegler-Natta catalyst systems based on titanium, cobalt or nickel compounds in conjuction with reducing agents such as aluminium alkyls or alkyl halides. Useful rubbers may also be obtained by using lithium alkyl catalysts but in which the cis content is as low as 44%. 

Alkyl fluorides have been prepared by reaction between elementary fluorine and the paraffins, by the addition of hydrogen fluoride to olefins, by the reaction of alkyl halides with mercurous fluoride, with mercuric fluoride, with silver fluoride, or with potassium fluoride under pressure. The procedure used is based on that of Hoffmann involving interaction at atmospheric pressure of anhydrous potassium fluoride with an alkyl halide in the presence of ethylene glycol as a solvent for the inorganic fluoride a small amount of olefin accompanies the alkyl fluoride produced and is readily removed by treatment with bromine-potassium bromide solution. Methods for the preparation of alkyl monofluorides have been reviewed. ... 

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