1,6-Hofmann elimination quaternary

The Hofmann elimination route, of which many versions exist, can be carried out at much lower temperatures in conventional equipment. The PX is generated by a 1,6-Hofmaim elimination of amine from a quaternary ammonium hydroxide in the presence of a base. This route gives yields of 17—19%. Undesired polymeric products can be as high as 80% of the product. In the presence of a polymerization inhibitor, such as phenothiazine, DPXN yields can be increased to 50%. 

Quaternary ammonium hydroxides undergo elimination on being heated. It is an anti elimination of the E2 type. The regioselectivity of the Hofmann elimination is opposite to that of the Zaitsev rule and leads to the less highly substituted alkene. 

Hofmann elimination (Section 22.14) Conversion of a quaternary ammonium hydroxide, especially an alkyltrimethyl-ammonium hydroxide, to an alkene on heating. Elimination occurs in the direction that gives the less substituted double bond. 

The preparation of an alkene 3 from an amine 1 by application of a /3-elimination reaction is an important method in organic chemistry. A common procedure is the Hofmann elimination where the amine is first converted into a quaternary ammonium salt by exhaustive methylation. Another route for the conversion of amines to alkenes is offered by the Cope elimination. 

The Hofmann elimination reaction is not often used today in the laboratory, but analogous biological eliminations occur frequently, although usually with protonated ammonium ions rather than quaternary ammonium salts. In the biosynthesis of nucleic acids, for instance, a substance called adenylosuccinate... 

Qiana, structure of, 836 Quantum mechanical model, 4-6 Quartet (NMR), 460 Quaternary ammonium salt. 917 Hofmann elimination and, 936-937... 

ALKENES via HOFMANN ELIMINATION USE OF ION-EXCHANGE RESIN FOR PREPARATION OF QUATERNARY AMMONIUM HYDROXIDES DIPHENYLMETHYL VINYL ETHER... 

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-... 

Aryl vinyl ketones are produced thermally from the corresponding quaternary ammonium salts via Hofmann elimination. However, the conjugated ketones are heat-sensitive and polymerization is difficult to avoid. Traditional preparations afforded only moderate yields. Microwave conditions were established for Hofmann eliminations, performed essentially quantitatively, by batch or continuous processes. 

Hofmann elimination, quaternary ammonium compounds, 2 737 Hofmann-Gerhardt nomenclature,... 

Sodium hypochlorite reacts with (1) to give the 1-chloro derivative, which gives rise to a variety of products, including the bicyclic amine, pyrrolizidine, when treated with silver salts (72CJCH67). Quaternary salts derived from (3) react with sodium methoxide to give mostly the acyclic Hofmann elimination product (83%) minor amounts of (3) (14%) are also formed, together with a trace (2%) of the product of 5N2 attack on the a-methylene carbon (80JOC3952). 

The successful synthesis of furanophane (27) by pyrolysis of the quaternary ammonium hydroxide (28) (60JA1428) has prompted the adaptation of this 1,6-Hofmann elimination procedure to the synthesis of numerous heterophanes (77CRV513,77H(7)81,78T1641). Fluoride anion-induced 1,6-elimination of (29) or (30) gives (27) or (31) and (32), respectively, in good yields (81JOC1043). 

Base-catalysed quaternary ammonium salts give alkenes and 3° amines. This reaction is known as Hofmann elimination or Hofmann degradation. Amines can readily be converted to quaternary ammonium salt by the treatment of excess primary alkyl halides, and then Ag20 and H2O. Quaternary ammonium salts undergo E2 elimination, when heated with NaOH to give alkenes and tertiary amines. Thermal decomposition of a quaternary ammonium salt by NaOH to an alkene is known as Hofmann elimination. 

Manufacture. For the commercial production of DPXN (di-/)-xyIylene) (3), two principal synthetic routes have been used the direct pyrolysis of p-xylcnc (4, X = Y = H) and the 1,6-Hofmann elimination of ammonium (HNR ) from a quaternary ammonium hydroxide (4, X = H. Y = NR ). Most of the routes to DPX share a common strategy PX is generated at a controlled rate in a dilute medium, so that its conversion to dimer is favored over the conversion to polymer. 

The base-promoted elimination of quaternary ammonium ions (Hofmann elimination) has been proposed to proceed by an E2-like mechanism. Tell how each of the following observations supports this mechanistic classification. Be specific about exactly what each piece of information reveals. 

Here, we envisage building the benzimidazole scaffold directly onto the linker and, by analogy with a regular tertiary amine synthesis on the REM linker, we can quaternize the resin-bound benzimidazole compounds by reaction with reactive bromides. The quaternary salt can then be liberated by a Hofmann elimination reaction upon treatment with base. 

Quaternary ammonium hydroxides undergo Hofmann elimination when they are heated. A point to be considered here concerns the regioselectivity of Hofmann eliminations it is the less hindered / proton that is removed by the base giving the less substituted alkene. 

Hofmann elimination has been used as a tool in structure proof (see dauriso-line, Section II,C,19, and 2 -/V-methylberbamine, Section II,C,62). Unintentional Hofmann elimination of quaternary bases can be brought about by excess diazomethane (257). The reported process for dequatemization of tubocurarine... 

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