Menthol mechanism

These observations throw light on the mechanism which governs the transformation in the plant of the compounds belonging to the menthol group. This alcohol being produced simultaneously with the green parts of the plant, is partially esterified in the leaves the esterification here... 

Fischer alkenylcarbene complexes undergo cyclopentannulation to alkenyl AT,AT-dimethylhydrazones (1-amino-1-azadienes) to furnish [3C+2S] substituted cyclopentenes in a regio- and diastereoselective way along with minor amounts of [4S+1C] pyrrole derivatives. Enantiopure carbene complexes derived from (-)-8-(2-naphthyl)menthol afford mixtures of trans,trans-cycloipentenes and ds,ds-cyclopentenes with excellent face selectivity [75]. The mechanism proposed for the formation of these cyclopentene derivatives is outlined in Scheme 28. The process is initiated by nucleophilic 1,2-attack of the carbon... 

A 5-1. three-necked round-bottomed flask is fitted with a mechanical stirrer (Note 1) and a reflux condenser bearing a calcium chloride tube. A solution of 400 g. (2.56 moles) of -menthol (crystals, m.p. 41-42°) in 11. of dry toluene (Note 2) is placed in the flask, and to it is added 70 g. (3.04 gram atoms) of clean... 

In order to explain the formation of nortricyclene from 2-ea o-norbornanol, it is necessary to assume a back side attack at the hydrogen attached to carbon 6. The general mechanism here is similar to the trans elimination reaction as discussed under menthol, 1,4-cyclohexanediol, and bornanols. 

The sweet taste and olfactory responses to a variety of stimuli are examples of chemical senses that utilize protein receptors for initial detection of the stimulus. Most bitter compounds have a hydrophobic component which enables their direct interaction with the cell membrane however, some evidence suggests a protein receptor mechanism. The cooling sensation is treated as a chemesthetic sense, where stimulation takes place at the basal membrane. However, compounds that evoke this response have very specific structural limitations, and most are related to menthol. For purposes of discussion, bitter and cooling sensations will be discussed under generalized receptor mechanisms. 

Optically active acrylic, chloro-acrylic and methacrylic esters of sec. butyl alcohol, 2-methyl-butyl alcohol, 1.3-dimethyl-butyl alcohol, 1-methyl-benzyl alcohol, bomeol and menthol have been polymerized mostly by radical mechanism (Tables 16, 17, 18). 

These two diastereoisomeric cyclohexyl chlorides derived from menthol react very differently under the same conditions with sodium ethoxide as base. Both eliminate HC1 but diastereoisomer A reacts rapidly to give a mixture of products, while diastereoisomer B (which differs only in the configuration of the carbon atom bearing chlorine) gives a single alkene product but very much more slowly. We can safely exclude El as a mechanism because the same cation would be formed from both diastereoisomers, and this would mean the ratio of products (though not necssarily the rate) would be the same for both. 

Like the synthesis of L-DOPA by asymmetric hydrogenation, the manufacture of L-menthol hy Takasago Company is also one of the early examples of an industrial process where asymmetric isomerization is a key step. The desired isomerization reaction is one of the steps of the overall synthetic scheme. The synthesis of L-menthol from diethyl geranylamine is shown by 9.2. The formal electron pair pushing mechanism for the isomerization of the allylic amine to the enamine proceeds according to reaction 9.3. 

In a i-l. round-bottom flask provided with a mechanical stirrer is placed 120 g. (0.4 mole) of crystallized sodium dichromate (or an equivalent amount of potassium dichromate), and to this is added a solution of 100 g. (0.97 mole) of concentrated sulphuric acid (sp. gr. 1.84) in 600 cc. of water. To this mixture 90 g. (0.57 mole) of menthol (crystals, m. p. 41-420) is added in three or four portions and the mixture stirred (Note 1). Heat is evolved and the temperature of the mixture rises to about 550 (Note 2). As soon as the reaction is complete the temperature falls. The oil is mixed with an equal volume of ether, separated in a separatory funnel, and washed with three 200-cc. portions of 5 per cent sodium hydroxide solution (Note 3). The ether is then removed by distillation and the residue distilled under reduced pressure, the menthone being collected at 98-100°/i8 mm.. If distilled under atmospheric pressure it boils at 204-207 The yield is 74-76 g. (83-85 per cent of the theoretical amount). 

This isomerization is enantioselective when optically active BINAP is used and provides practical access to optically active aldehydes and alcohols such as L-menthol, which is a key fragrance chemical [297—299], The proposed mechanism involves amine, iminium, and enamine as complex intermediates [300], Extension of this olefin isomerization is realized in the isomerization of an alkyne to a conjugated diene (Scheme 1-47) [301], High chemoselectivity is achieved when Pd(OAc)2 or [Pd2(dba)3]/HOAc, in the presence of phosphine, is used as catalyst (Table 1-14). The phosphine of choice is dppb although dppf could give a similar yield. 

The only product in this category that has been adequately studied is Listerine. Listerine is a mixture of essential oils—thymol, menthol, a eucalyptol, and methylsalicylate. The mechanism of action appears to be related to alteration of the bacterial cell wall. This product is uncharged and has a low substantivity. Adverse effects reported have been a burning sensation and bitter taste. It is available in a 21.6-26.9% alcohol vehicle with a pH of 4.2. Recommended usage is twice daily, and the ADA accepts the product and some of its generic copies for the control of plaque and gingivitis. 

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