Question

What carboxylic acid would be formed if the malonic ester synthesis (alkylation of diethyl malonate followed by hydrolysis with acidic workup and decarboxylation) were carried out with one equivalent of malonic ester, one equivalent of 1,5-dibromopentane, and two equivalents of hydroxide as the base

Answer 1

Using malonic ester synthesis with 1,5-dibromopentane and hydroxide leads to the formation of hexanoic acid after the alkylation, hydrolysis, and decarboxylation steps.

Step-by-step explanation:

The malonic ester synthesis involves the alkylation of diethyl malonate, which in turn involves the reaction of diethyl malonate with an alkyl halide in the presence of a base. Subsequent hydrolysis and decarboxylation steps lead to the formation of a substituted acetic acid. When diethyl malonate reacts with 1,5-dibromopentane using hydroxide ions as the base, the alkylation at one of the methylene groups next to the ester functionalities gives rise to a pentyl-substituted malonic ester. After hydrolysis in an acidic medium and decarboxylation, the carboxylic acid obtained would be hexanoic acid (caproic acid), which has a six-carbon chain.

Answer 2

cyclohexilic acid

Step-by-step explanation:

The malonic ester synthesis is often used to form different types of carboxilic acid. In this case, we have excess of base, so we can expect a ring formed in the molecule.

In the first step, the base substract the more acidic hydrogen of the ester. In the next step we have the ester reacting with the dibromopentane. Then, in the next step, the excess of base will substract again the acidic hydrogen remaining of the carbon, and then, will promove a Sn2 reaction with the bromine in the pentane (That it was previously attached to the molecule). In this step, a ring id formed. Then, the hydrolisis with acid, will form carboxilic acid in both sides of the molecule, and finally the decarboxilation in heat will separate the molecule and formed the cyclohexilic acid.

The picture below shows the mechanism