Un saturated hydrocarbons

All the products of Clemmensen reductions contain small amounts of un-saturated hydrocarbons. These can be removed by repeated shaking with 10 per cent, of the volume of concentrated sulphuric acid until the acid is colourless or nearly so each shaking should be of about 5 minutes duration. The hydrocarbon is washed with water, 10 per cent, sodium carbonate solution, water (twice), dried with anhydreus magnesium or calcium sulphate, and finally distilled twice from a Claisen flask with fractionating side arm (or a Widmer flask) over sodium. 

There are formed also a little octane, dodecane, and un-saturated hydrocarbons. 

On the basis of three facts—that no change in the carbon skeleton occurs during the reactiim that all members of a family of isomeric aliphatic carbonyl compounds, differing from one another only in the position of the oxygen atom, form the same final product and that un-satUrated hydrocarbons can undergo reactions very similar to the... 

The lack of reactivity of acyl cations such as the acetyl cation with deactivated aromatics or saturated hydrocarbons is therefore not un-... 

This and other similar cycloadditions, however, when unactivated hydrocarbons without heteroatom substituents participate in Diels-Alder reaction, are rarely efficient, requiring forcing conditions (high temperature, high pressure, prolonged reaction time) and giving the addition product in low yield. Diels-Alder reactions work well if electron-poor dienophiles (a, p-un saturated carbonyl compounds, esters, nitriles, nitro compounds, etc.) react with electron-rich dienes. For example, compared to the reaction in Eq. (6.86), 1,3-butadiene reacts with acrolein at 100°C to give formy 1-3-cyclohexene in 100% yield. 

The saturated fatty acids that are present in significant quantities in milk fat are molecules with un-branched hydrocarbon chains, which vary in length from 4 to 18 carbon atoms. These fatty acids account for approximately 70 to 75% of the total fatty acids. The most important saturated fatty acid from a quantitative viewpoint is 16 0, which accounts for about 25 to 30% of the total, while two other fatty acids, 14 0 and 18 0 have values in the region 10 to 13% (Table 1.2). The amounts of the short-chain fatty acids, 4 0 and 6 0, are reasonably high when their proportions are expressed as molar percentages (approximately 10 and 5%, respectively—Table 1.2) appreciable amounts of medium-chain length fatty acids (Cs to C12) are also present. 

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