Alcohols and Phenols

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DISCUSSION

Alcohols are compounds containing the hydroxyl (-OH) functional group bonded toan alkyl, R and thus may be represented by the general formula: ROH.

The reactivity of alcohols is mainly attributed to the -OH group. This functional group has an inherent acid character shown when the hydrogen is released from the OH bond. The case of removal is dependent upon the relative polarization of the O-H bond. The -OH group may also be protonated at the oxygen, which weakens the C-O bond so that the whole group may be cleaved off as a water and subesequently replaced in the molecule.

Primary and secondary alcohols may be distinguish from tertiary alcohols by the chromic acid test. Primary alcohols are oxidized to aldehydes while secondary alcohols are oxidized to ketones. This indicated by the color of the solution from orange to green. Tertiary alcohols are not readily oxidized by the chromic acid because of the absence of the alpha hydrogen.

Phenols are aromatic compounds with -OH groups directly bonded to the ring. The general formula is ArOH. Phenol is prepared in the laboratory by the diazotization of primary aromatic amines. The acidic charecter of the -O-H group is very well observed in phenols. They are more acidic than alcohols due to the resonance stabilization. The negative charge of the conjugate base, phenoxide ion, is delocalized through the benzene ring. Although phenol is acidic enough to react with sodium hydroxide to form sodium phenoxide, it is not strong enough to react with with sodium carbonate.

Unlike alcohols, phenols do not react directly with carboxylic acids to form esters. Esters of phenols can be prepared with carboxylic acid anhydride or with acid halides in the presence of a base or acid as a catalyst. Phenol gives a violet or dark blue color when treated with a diute solution of ferric chloride. The color is due to the ferric phenoxide salts, which absorb visible light to give an excited state having electrone delocalized both over the iron atom and the unsaturated system.

QUESTIONS:

1. Differentiate alcohols and phenols based on their properties

Phenols are the aromatic organic compounds that have a hydroxyl group directly connected to a ring. While alcohols are the non-aromatic compounds that have hydroxyl group connected to the main chain.

2. What does the chromic acid test indicates? Lucas test?

It indicates whether the alcohols are primary, secondary, or tertiary.

3. Explain why Lucas test is applicable only to alcohols containing not more than 5 carbons?

Lucas test is only applicable to alcohols containing ot more than 5 carbons because due to the fact that the alcohols w/ 5 or less carbons are water soluble but alcohols with more carbons are water insoluble and are itself turbid. Turbid or turbidity is the cloudiness or haziness of a fluid caused by large numbers of individual particles that are generally invisible to the naked eye.

4. Compare the relative case of oxidation of 1º, 2º, 3º alcohols towards acid dichromate based on the time required for the solution to change color?

The primary has a faster reaction and the tertiary has the slowest reaction in changing color.

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