What alkyl bromide(s) should be used in the malonic ester synthesis of each of the following car

What alkyl bromide(s) should be used in the malonic ester...

Key Concepts

Malonic Ester Synthesis

This is a classic method for constructing substituted acetic acids (and thereby carboxylic acids) from diesters such as diethyl malonate. In the process, the active methylene group between two ester groups is deprotonated, then alkylated using an alkyl halide to introduce a carbon substituent. Subsequent hydrolysis and decarboxylation yield a carboxylic acid where the alkyl substituent and an additional methylene (derived from the malonate) have combined to form the final carbon skeleton.

SN2 Alkylation Reaction

At the core of malonic ester synthesis is the SN2 reaction in which the enolate derived from diethyl malonate attacks an alkyl halide (such as an alkyl bromide) to form a new carbon–carbon bond. This step is sensitive to steric hindrance, so primary (or in some cases methyl) halides are typically employed to achieve efficient alkylation.

Decarboxylation Process

After alkylation and subsequent hydrolysis, the intermediate malonic acid derivative undergoes decarboxylation. This reaction, typically promoted by heating, removes one carboxyl group as carbon dioxide, thus forming a substituted acetic acid. The decarboxylation step is key to simplifying the molecule’s carbon framework and finalizing the acid synthesis.

Retrosynthetic Analysis

This is the process of deconstructing a target molecule (a carboxylic acid, in this context) into simpler precursor fragments. In malonic ester synthesis, retrosynthesis involves recognizing that the final acid is formally derived from an alkylated malonic ester intermediate, where the pattern RCH2COOH implies that the alkyl group R must be chosen so that, after insertion of a methylene group and loss of CO2, the desired carbon skeleton is obtained.

Transcript

00:01 Okay, so we have to use melanic ester synthesis to create the following compounds, and we have to decide what alkali to use.

00:08 So the bolognaic ester looks like this, and at the end of the reaction, we're always going to have a two -carbon carbon dioxide.

00:19 So the first step is that we treat this with a strong base to depotinate the alpha hydrogen.

00:30 So we get a carbaneion again.

00:36 And then, so at the end, we'll have a two -carbon carbon dioxide, so we need one more carbon for the product.

00:43 Which is propinolc acid.

00:46 So we're going to react this with methyl bromide.

00:50 It's going to attack the methyl and expel the bromine.

01:00 So now we actually have our products.

01:02 We just need to get rid of the esters and eventually the carbox silk acid, the one carbox silk acid.

01:11 So treating it with hcl and water over heat is going to get rid of, we'll turn the esters into alcohols.

01:25 So we have the methyl right here for methyl bromide.

01:28 And then treating this with heat, decarboxylation is going to occur.

01:37 So we'll lose co2, and we'll get our products.

01:44 So you have one, two, three propionic acid, and we'll get co2 as a side product.

01:55 That's the first one.

01:57 The second one, just starting with the mlonicester, we want to create two methyl propanolac acid.

02:14 So the first step is always the same, reacting with a strong base to deprinate the alpha hydrogen.

02:20 So we need two more carbons.

02:30 We need two methyl added to this carbon right here.

02:35 So we'll react it with methyl bromide twice.

02:43 And then to turn the esters into carboxylacic acids, reacting with hcl and water, never heat.

02:55 And then four is to get rid of the one carboxylac acid.

02:59 So we're just heating it.

03:01 And we get a product...

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