Caproic Acid Synthesis

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Introduction
In this lab, caproic acid was synthesized in a multi-step process that involved the synthesis of three intermediates – diethyl n-butylmalonate, potassium n-butylmalonate, and n-butyl malonic acid respectively. An IR was used to characterize the starting material, n-bromobutane, and the first intermediate, diethyl n-butylmalonate; while IR and NMR were used to characterize the final product, caproic acid. Reactions, Mechanism and Theory

Caproic acid a.k.a n-hexanoic acid is a carboxylic acid derived from hexane which has the general formula C5H11COOH. It is a colorless oily liquid with a really pungent odor associated with goats. Caproic acid was synthesized in a multi-step process which produced three intermediates - diethyl n-butylmalonate, potassium n-butylmalonate, and n-butyl maonic acid. The synthesis of caproic acid involved alkylation, saponification, and decarboxylation reactions. The first intermediate, diethyl n-butylmalonate – a diethyl ester of malonic acid – was synthesized via an alkylation reaction. Alkylation reactions involve the formation and alkylation of an enolate. In this lab, NaOEt, a strong base was used to pull off one of the most acidic α-hydrogens of the carbonyl ester – diethylmalonate – to form an enolate. In order to alkylate the alpha position which now has a negative charge, the enolate was used to attack an alkyl halide, 1-bromobutane via Sn2 mechanism. The mechanism for the above reaction is shown below:

The second intermediate, potassium n-butylmalonate, was synthesized by saponification of the first intermediate, diethyl n-butylmalonate, with potassium hydroxide. The hydrolysis of diethyl n-butylmalonate resulted in the formation of potassium n-butyl malonic acid by losing the ethoxy group (-OCH2CH3) from both sides of the carbonyl ester. Further deprotonation of the formed acid by -OCH2CH3 forms a carboxylate, potassium n-butylmalonate. The mechanism for the above process is shown below:

N-butyl malonic acid, the third intermediate, was immediately synthesized from the potassium n-butylmalonate by the protonation of potassium n-butylmalonate via the addition of excess HCl as shown below:

The final step of this lab involved the decarboxylation of n-butyl malonic acid to form caproic acid. Decarboxylation is the removal of a carboxyl group, -COOH, from a carbonyl compound to form CO2 and an enol which further tautomerizes to form a ketone. In this lab, the removal of a -COOH from the n-butyl malonic acid formed 1,1-dihydroxy-hex-1-ene. Tautomerization of this product leads to the formation of caprioc acid. the above reaction mechanism is shown below:

Reagent Tables
Table 1: Synthesis of diethyl n-butylmalonate (Reagents and Product) Name| Chemical Formula| Molecular Weight| Density(g/ml)| Conc(M)| Amount(g or ml)| Amount(moles)| Melting Point(0C)| Boiling Point(0C)| Sodium Ethoxide| NaOEt| 68.05| 0.868| | 50ml9.1187g| .134| 260| ---| Diethyl malonate| | 160.17| 1.055| | 20.34ml21.46g| .134| -50| 199| 1-Bromobutane| n-BuBr| 137.02| 1.270| | 14.5ml18.36g| .134| 1.2686| 101.4| Absolute Ethanol| EtOH| 46.07| 0.789| | 35ml| | -114.3| 78.4| Ether| Et2O| 74.12| 0.7134| | | | -116.3| 34.6|

Water| H2O| 18.1| 1000| | | | 0| 100|
Magnesium sulfate| MgSO4| 120.415| 2.66| | | | 1124| ---| Diethyl n-butylmalonate| C11H20O4| 216.28| 0.983| | | | ----| 235 -240| Table 2: Synthesis of Potassium n-butylmalonate (Reagents and Product) Name| Chemical Formula| Molecular Weight(g/mol)| Density(g/ml)| Conc(M)| Amount(g or ml)| Amount(moles)| Melting Point(0C)| Boiling Point(0C)| Diethyl n-butylmalonate| C11H20O4| 216.28| 0.983| | | | ---| 235 -240| Potassium hydroxide| KOH| 56.11| 2.044| | | | 420| 1327| Water| H2O| 18.1| 1000| | | | 0| 100|

Sodium Chloride| NaCl| 58.443| 2.165| | 35ml| | 801| 1413| Potassium n-butylmalonate| | | | |...
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