Alkenes from ammonium hydroxides

A little used synthesis of primary alkylamines is the amination of organoboranes. Organoboranes have now been shown to react with chloramine-T prepared in situ from ammonium hydroxide and sodium hypochlorite to give the corresponding amines (Scheme 5). This procedure then represents a mild, one-pot synthesis of various primary alkylamines from alkenes. 

Olefins, sultones, alkanes, and alkenesulfonates may be separated by liquid chromatography on silica gel using hexane, trichloromethane-hexane, ethanol-dime thy lcarbonate, and ethanol-ammonium hydroxide as the eluents. Pueschel and Prescher [110] achieved the separation of alkene-1,4-sultone and alkene-1,3-sultone from each other and from other sulfonic acid esters in AOS by thin-layer chromatography on silica gel G with 4 1 diethylcarbonate-ligroine as the... 

The Hofmann elimination is useful synthetically for preparing alkenes since it gives the least substituted alkene. The reaction involves thermal elimination of a tertiary amine from a quaternary ammonium hydroxide these are often formed by alkylation of a primary amine with methyl iodide followed by reaction with silver oxide. The mechanism of the elimination is shown in Scheme 1.13 in this synthesis of 1-methyl-1-... 

PTC has been extensively used for making cyclopropyl derivatives. The most common reaction involves generation of dichlorocarbene from chloroform, using NaOH and a quaternary ammonium hydroxide. The carbene subsequently reacts with an alkene in high yield. Hydrolysis of dichlorocarbene, normally rapid in the presence of water, is minimal. An interesting and very efficient example of a Michael addition to produce a cyclopropyl derivative is shown in Scheme 4.26. 

The elimination of hydrogen halide from organic halides under basic conditions generates alkenes and is a fundamental reaction in organic chemistry. It is sometimes carried out with a base in aqueous media.14 In contrast, the corresponding Hofmann-type eliminations of quaternary ammonium hydroxides are frequently carried out in aqueous media,15 which will be covered in Chapter 11. 

The kinetic preference for cis- over imns-olefin elimination from acyclic compounds is rare. Cope and co-workers 91) reported a slight preference for cis- over irans-2-butene and 2-pentene in the thermal decomposition of the quaternary ammonium hydroxides, and Andr u and co-workers 92,93) found a preponderance of cis- over trons-2-butene in the elimination of hydrogen chloride from 2-chlorobutane over solid catalysts. Neureiter and Bordwell 94) found the formation of cis-2-butene rather than alkene from a-chlorosulfone on treatment with alkali ... 

Apart from the reactions of diazonium salts, a number of other reactions are known in which the C-N bond is broken. The best known of these is the Hofmann elimination of quaternary ammonium hydroxides (Scheme 2.37). An amine is converted by methylation with methyl iodide to the quaternary ammonium salt ( exhaustive methylation ). The iodide, on treatment with moist silver oxide, forms the quaternary ammonium hydroxide which undergoes a bimolecular elimination to form an alkene. The bimolecular elimination of onium salts yields the least alkylated alkene. This substitution pattern is determined by the ease with which a hydrogen atom can be attacked by the base. 

The reaction between epoxides and ammonia (or ammonium hydroxide) is a general and useful method for the preparation of (3-hydroxyamines. With epoxide derived from terminal alkenes, the reaction with ammonia gives largely the primary amine, but secondary and tertiary amine products are possible from the appropriate epoxide. The reaction of 121 with ammonium hydroxide with microwave irradiation, for example, gave 122. Ethanolamines, which are useful solvents... 

When heated, a quaternary ammonium hydroxide undergoes elimination to an alkene and a tertiary amine. From the structures of these products it is often possible to deduce the structure of the original amine. As a simple example, contrast the products (1 and II) obtained from the following isomeric cyclic amines ... 

As stated previously, compound B was the alkene (actually a diene) that resulted from the decomposition of the quaternary ammonium hydroxide. Hence, the hydroxide had to have the formula of ... 

The thermal decomposition of a quaternary ammonium hydroxide to alkene, tertiary amine and water was first observed by Hofmann in 1851 (equation 2) From his work with unsymmetrical amines. 

Two isomeric alkenes form in a 10 1 ratio when the quaternary ammonium hydroxide derived from 1-methylcyclohexylamine and methyl iodide is heated, (a) Draw the structures of the isomers, (b) Which one forms in the larger amount ... 

Diols.—The osmium tetroxide-catalysed y/c-hydroxylation of alkenes to provide cis- 1,2-diols, using t-butyl hydroperoxide in a basic medium (tetraethyl-ammonium hydroxide) to recycle Os to Os ", itself an advance over earlier methods, has been further improved by eliminating the need for strongly basic conditions. It has been reported that tetraethylammonium hydroxide may be replaced by the corresponding acetate if the solvent is simply changed from t-butyl alcohol to acetone, and that base-sensitive groups such as esters can survive the new conditions. 

Examples of the Michael-type addition of carbanions, derived from activated methylene compounds, with electron-deficient alkenes under phase-transfer catalytic conditions have been reported [e.g. 1-17] (Table 6.16). Although the basic conditions are normally provided by sodium hydroxide or potassium carbonate, fluoride and cyanide salts have also been used [e.g. 1, 12-14]. Soliddiquid two-phase systems, with or without added organic solvent [e.g. 15-18] and polymer-supported catalysts [11] have been employed, as well as normal liquiddiquid conditions. The micellar ammonium catalysts have also been used, e.g. for the condensation of p-dicarbonyl compounds with but-3-en-2-one [19], and they are reported to be superior to tetra-n-butylammonium bromide at low base concentrations. 

The synthesis of 1,1-diiodocyclopropane is carried out via addition of diiodocarbene (car-benoid) to alkenes the carbene, in turn, is generated from iodoform and a base. The process is realized using phase-transfer catalysis,(33% or 50%aqueous sodium hydroxide and a quaternary ammonium salt, typically benzyltriethylammonium chloride, as a catalyst) or in the presence of potassium ter/-butoxide in /ert-butyl alcohol 25,127,128 g... 

There is another type of elimination, and the contrast with an E2 reaction is clear in the experiment that heats ammonium salt 42 [2-(trimethylammonium) butane hydroxide] to about 200°C, neat (no solvent). The product is 1-butene (43) isolated in 95% yield. The remainder of the product (5%) was a mixture of cis- and ra/ s-2-butene (44). Water and triethylamine are also products of this reaction. This is clearly an elimination reaction, but the major product is the less stable alkene, which is exactly opposite from the results obtained in an E2 reaction. There are two P-hydrogen atoms in 42—Hg and H,—but the only way to obtain water, triethylamine and 43 is by removal of from the methyl group of 42. 

The phase-transfer catalyst is soluble in both water and the organic solvent. It is water soluble because it is an ion, and it is hexane soluble because of the three long-chain alkyl groups. Thus, the phase-transfer catalyst distributes itself in both phases, and freely shuttles back and forth through the phase boundary between solvent layers. In aqueous NaOH, the chloride anion exchanges with hydroxide anion, as the counterion to the ammonium cation. When it does this, the catalyst carries the hydroxide ion from the aqueous phase, as an ion-pair, across the phase boundary into the organic phase, where the base then reacts with the diethyl benzylphosphonate. The Homer-Wadsworth-Emmons reaction then occurs, producing the alkene and diethyl phosphate anion. This anion becomes associated with the ammonium cation of the phase-transfer catalyst and is transported to the aqueous layer, where the catalyst picks up another hydroxide ion and repeats the entire process. 

Butylation of phenylacetonitrile with aqueous NaOH, as shown in Scheme 25, proceeds faster by use of high DF (>0.5) anion exchange resins.The strongly alkaline conditions degrade the quaternary ammonium ions of the catalyst. Catalyst (64) (1% DVB) is active for alkylation of phenylacetonitrile and benzyl phenyl ketone, and for Williamson ether synthesis, and it is much more stable in base than AERs. AERs in OH form are catalysts for dichlorocyclopropane syntheses from alkenes, chloroform and solid sodium hydroxide, and for dehydration of amides to nitriles. AERs in the appropriate hydroxide, acetate, or cyanide form are catalysts for aldol condensations, Michael reactions, Knoevenagel condensations, cyanoethylations and cyanohydrin syntheses. " ... 

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