The four-member ring in α-pinene makes it a reactive hydrocarbon, prone to skeletal rearrangements such as the Wagner-Meerwein rearrangement. For example, attempts to perform hydration or hydrogen halide addition with the alkene functionality typically lead to rearranged products. of under acidic conditions. With concentrated sulfuric acid and ethanol the major products are terpineol and its ethyl ether, while glacial acetic acid gives the corresponding acetate ester. With dilute acids, terpin hydrate becomes the major product.
With one molar equivalent of anhydrous HCl, the simple addition product can be formed at low temperature in the presence of ether, but it is very unstable. At normal temperatures, or if no ether is present, the major product is bornyl chloride, along with a small amount of fenchyl chloride. For many years (also called "artificial camphor") was referred to as "pinene hydrochloride", until it was confirmed as identical with bornyl chloride made from camphene. If more HCl is used, achiral (dipentene hydrochloride) is the major product along with some.
Nitrosyl chloride followed by base leads to the oxide 8 which can be reduced to "pinylamine" Both and are stable compounds containing an intact four-member ring, and these compounds helped greatly in identifying this important component of the pinene skeleton. A variety of reagents such as iodine or PCl3 cause aromatization, leading to p-cymene .
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