Alcohol & Phenol Reactions

Alcohol Reactions 1. Dehydration - elimination of water water is eliminated from adjacent carbon atoms and a second bond is formed between the 2 carbon atoms uses a large amount of alcohol and a small amount of acid (H 2 SO 4 ) as the catalyst order of reactivity: – tertiary > secondary > primary

Dehydration Examples 1.Dehydrate butanol. 2.Dehydrate 2-butanol. 3. Dehydrate 2-methyl-2-butanol.

2. Halide Substitution - alcohols react with concentrated hydrohalogens (HCl, HBr, HF) to be converted into alkyl halides competes with the elimination reaction (dehydration) but this reaction is favored using a large excess of concentrated acid (HCl and zinc chloride) we can distinguish between 1 °, 2 ° and 3° alcohols by their different rates of reaction using the Lucas Test order of reactivity: – tertiary > secondary > primary

Halide Substitution Examples: The Lucas Test 1. Primary alcohols - are not converted to alkyl chlorides at room temp; dissolve completely 2. Secondary alcohols – dissolves, but within 5 minutes, the alkyl chloride separates out 3. Tertiary alcohols – react immediately; the insoluble tertiary alkyl chloride separates out as a cloudy layer

3. Esterification – alcohols react with carboxylic acids to form esters and water esters – compounds in which the proton of an acid is replaced by an organic group General formula is Esters are named as derivatives of BOTH the carboxylic acid and the alcohol – The 1 st word denotes the alcohol group (R) and is named like a hydrocarbon with a –yl ending – The 2 nd word is derived from the name of the parent acid, with the “-ic acid” ending changed to an “-ate” ending.

Esterification Examples Ex.1 React methanol with acetic acid. Ex.2 React propanol with butanoic acid. Ex.3 React 2-propanol with butanoic acid.

4. Oxidation - the most important method of preparing aldehydes, ketones and carboxylic acids from alcohols Uses Jones Reagent in what is called the Bordwell-Wellman Test Jones Reagent – made by dissolving CrO 3 in water with H 2 SO 4 to give chromic acid, which is orange in color aldehyde ketone carboxylic acid

Oxidation Examples Primary alcohols - oxidized in a 2-step process to first give an aldehyde, and then an acid Ex.; Oxidize ethanol. Secondary alcohols - oxidized to form ketones Ex.; Oxidize 2-butanol. Tertiary alcohols - have no C-H bonds on the hydroxyl carbon, therefore they cannot undergo oxidation. Ex.; Oxidize tert-butanol.

Reactions of Phenols Phenols DO NOT undergo dehydration or substitution reactions because it is very hard to break the C-O bond when the carbon atom is part of an aromatic ring They will form esters because the O-H bond is breaking, not the C-O bond

1. Esterification - phenol reacts with an acid anhydride (two acid molecules with a water removed) to form a carboxylic acid and an ester Ex.; part a: form acetic anhydride part b: react phenol with acetic anhydride

2. Oxidative Coupling - uses potassium ferricyanide, K 3 Fe(CN) 6, as the catalyst -three types of coupling: ortho-ortho, ortho-para, and para-para Ex. React phenol with K 3 Fe(CN) 6. Ex. React p-methylphenol with K 3 Fe(CN) 6.