Alkane derivatives alkyne hydrogenation

There are four subfamilies of hydrocarbons, known as alkanes, alkenes, alkynes, and aromatics. (These families will be discussed in detail in Chapters 4 and 5.) The alkane and aromatic families of hydrocarbons occur naturally the alkenes and alkynes are manmade. Both types of hydrocarbons are used to make other families of chemicals, known as hydrocarbon derivatives. Radicals of the hydrocarbon families are made by removing at least one hydrogen from the hydrocarbon and replacing it with a nonmetal other than carbon or hydrogen. Ten of these hydrocarbon derivatives will be discussed in detail in the appropriate chapters associated with then-major hazards alkyl halides, nitros, amines, ethers, peroxides, alcohols, ketones,... 

Several of the trialkylaluminum and alkylaluminum halides and hydrides mentioned above are commercially available. Alkynyl, alkenyl, cyclopentadienyl, and aryl derivatives are, in general, not commercially available and must be synthesized for laboratory use. Alkynyl derivatives can be prepared by salt metathesis, as in the reaction of Et2AlCl with NaC=CEt to give Et2AlC=CEt. The acidity of terminal alkynes is sufficient for preparation of alkynyl aluminum compounds by alkane or hydrogen elimination upon reaction with a trialkylaluminum or an aluminum hydride (equation 17), respectively. TriaUcynyl aluminum compounds are typically isolated as Lewis base adducts to stabilize them against otherwise facile polymerization. Alkenyl compounds of aluminnm have similarly been prepared. 

Consider the C-H bond in alkanes. Carbon is a more electronegative element than hydrogen. Consequently, the electron pair that forms this bond is shifted towards the carbon atom. In the extreme, an ionic representation of this bond can be given as pictured in 122 (Scheme 2.45). Within these conventions the carbon atom in an alkane can be approximated as a carbanion (oxidation level 0 by definition). Using this definition it becomes possible to apply oxidation-reduction terminology to the processes as if they occurred to ion pair 122. Thus, oxidation of 122 with the loss of one electron leads to the radical 123. With the loss of two electrons, the oxidation leads to carbocation 124. Similarly, the conversion of an alkane to an alcohol and the alcohol into an aldehyde and the aldehyde eventually to a carboxylic acid can unambiguously be classified as an oxidation sequence with the loss of two, four, and six electrons. The oxidation levels 1, 2, and 3 are ascribed respectively to these functional derivatives. The conversion of an alkane to an alkene or alkyne can be interpreted in an analogous fashion. 

AU organic compounds are derived from a group of compounds known as hydrocarbons because they are made up only of hydrogen and carbon. On the basis of structure, hydrocarbons can be classified as aliphatic or aromatic. Aliphatic hydrocarbons do not contain the benzene group, or the benzene ring, whereas aromatic hydrocarbons contain one or more benzene rings. In addition, aliphatic hydrocarbons are further divided into alkanes, alkenes, and alkynes (Figure 16.1). 

---