Pinene-hydrochloride

Camphor was originally obtained from the camphor tree Lauras eamphora in which it appeared in the optically active dextro-rotary form. Since about 1920 the racemic ( ) mixture derived from oil of turpentine has been more generally used. By fractional distillation of oil of turpentine the product pinene is obtained. By treating this with hydrochloric acid, pinene hydrochloride (also known as bomyl chloride) may be produced. This is then boiled with acetic acid to hydrolyse the material to the racemic bomeol, which on oxidation yields camphor. Camphor is a white crystalline solid (m.p. 175°C) with the structure shown in Figure 22.3. 

It yields ordinary pinene hydrochloride when treated in the usual manner with hydrogen chloride. Verbenene and 8-pinene have the following constitutions —... 

Isopinene is a name which has been applied to at least two terpenes. Of these the earliest so-named is that isolated by Aschan by decomposing the liquid chlorides obtained in the process of preparing pinene hydrochloride, by the action of bases. He thus obtained a hydrocarbon which he termed pinolene, Cj Hj,., boiling at 145° to 146°. By converting... 

It yields a crystalline hydrochloride melting at 130° to 131°. This compound is much more easily volatilised than pinene hydrochloride. With chlorine it yields a dichlor-firpene hydrochloride, whilst pinene yields no similar compound. It also yields a crystalline hydrobromide melting at 102°. No crystalline nitrosochloride has been prepared. The melting... 

Camphene is extremely difficult to separate in the solid condition from essential oils, and it may therefore be taken for granted that natural camphene is rarely prepared in the pure condition. The figure given above for the specific rotation is for a sample artificially prepared from pinene hydrochloride. 

Pinene hydrochloride is prepared in the usual manner from turpentine, and this is allowed to react with acetate of silver. Isobornyl acatate is formed, which is hydrolysed, and the isoborneol oxidised to camphor. Acetate of lead is also used, as is also acetate of zinc. 

The action of magnesium on pinene hydrochloride gives rise to bomyl esters, and camphor can be obtained from these in the usual manner. 

Pinene hydrochloride is treated by one of the reagents which abstract-HCl, and so converted into camphene q.v.). This is heated with acetic and sulphuric acids, and so converted into isobornyl acetate. Canmhor results in the usual manner. 

Turpentine Oil.—This is readily recognised in oils which contain no pinene, as this is the main constituent of turpentine oil. It is usually found in the first distillates, and generally reduces the specific gravity and effects the solubility and optical rotation. Its presence is proved by the formation of pinene hydrochloride (melting-point 125°) and the nitro-sochloride (melting-point 103°). If pinene is a constituent of the oil itself, the addition of turpentine can only be proved by comparison with an authentic sample. 

The most straightforward method involves the conversion of pinene [l] into pinene hydrochloride [2], bornylchloride [3] and hence into borneol [6] (or iso-borneol) from which camphor [7] is obtained by oxidation. Also bornylchloride [3] is converted to isobro-nylacetate [5] upon heating with sodium acetate and glacial acetic acid. Alternatively, c-amphene [U] is oxidatively hydrated to camphor [7]-... 

Pinene Hydrochloride. Imitation Camphor.—This substance has an odor similar to camphor and it is known as imitation or artificial camphor but it is not synthetic camphor. When, however, pinene hydrochloride is treated with alcoholic potassium hydroxide a rearrangement takes place followed by hydrolysis and a terpene alcohol is obtained known as Bomeol. 

Derivation (1) By heating pinene hydrochloride with alkalies, aniline, or alkali salts such as sodium acetate. (2) A constituent of certain essential oils. 

In the case of hydrogen chloride addition to a-pinene (5.41), it is likely that the mechanism has a considerable degree of synchronous character for, if the free cation were to be formed, the molecule would rearrange as happens when pinene hydrochloride is allowed to warm up to room temperature. The reason for the instability of pinene hydrochloride... 

In our second puzzle, we begin with exactly the same series of reactions from a-pinene hydrochloride (5.46) to camphene (5.50) that we saw in Figure 5.31. They are repeated again in Figure 5.34 to emphasise the difference between the formation of bornyl chloride (5.46) from a-pinene and the formation of isobornyl chloride (5.55) from camphene (5.50). 

Berthelot s researches on the terpenes and camphor were important from the point of view of classification and he discovered some new compounds. He distinguished d- and /-pinene, calling them australene and terebentene, and d-, /-, and rf/-camphene, the last obtained by removing hydrogen chloride from pinene hydrochloride (bornyl chloride his camphene is now called bornylene). Berthelot used only the hydrochlorides to characterise the various pinenes. He... 

Scheme 7.47. A pathway using classical ions and the Wagner-Meerwein rearrangement as well as nonclassical ions to depict the formation of pinene hydrochloride (exo-2-chloro-2,6,6-trimethylbicyclo[3.3.1]heptane) from a-pinene (2,6,6-trimethylbicyclo[3.1.1]-2-heptene) and 3-pinene (2-methylene-6,6-dimethylbicyclo[3.3.1]heptane) and the subsequent interconversion of pinene hydrochloride (eA o-2-chloro-2,6,6-trimethylbicyclo[3.3.1]heptane) and bornyl chloride (enrio-2-chloro-l,7,7-trimethylbicyclo[2.2.1]heptane).

The facility and stereospecificity of the interconversions of the camphanyl, bornyl, and pinyl monoterpenes are renowned and provided the initial factual basis for the formulation of non-classical carbonium ion intermediates 39, 90). A tremendous number of investigations has been carried out upon the rearrangements of bicyclo[2.2.1]heptanes and the nature of the various carbonium ion intermediates 39). However, for the purposes at hand it will be sufficient to illustrate the characteristics of these rearrangements with the classical case of the camphene and pinene hydrochlorides (46-Cl and 47-Cl) rearrangements 91—93). 

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