DEET is the common name for N,N-diethyl-m-toluamide, a multipurpose insect repellent registered for — Organic Chemistry Chemistry Question

DEET is the common name for N,N-diethyl-m-toluamide, a multipurpose insect repellent registered for direct application to human skin. DEET is a unique pesticide because it is applied directly to the human body for the purpose of repelling insects. Because DEET was recognised as one of the few products that are effective against mosquitoes and biting flies, it was registered for use by the general public in the USA in 1957. Approximately 230 products containing DEET are currently registered with the Environmental Protection Agency manufactured by 70 different companies. Every year approximately one–third of the US population is expected to use DEET.

The characteristic features of DEET
* The chemical structure is shown below:
[VISUAL]
N,N-diethyl-m-toluamide
* Some physical properties are shown in the table below:
Density (25 °C) 0.996 g cm –3
Solubility in water practically insoluble
Solubility in other solvents soluble in ethanol, ether, chloroform, benzene
Boiling point (at 1 torr) 111 °C
Vapour pressure (160 °C) 19 torr
Odour odourless
Colour colourless

Synthesis of DEET
DEET can be prepared starting from m–methyl–benzoic acid (m–toluic acid). First, m–toluic acid is converted to the corresponding chloride. Next, the desired amide is prepared by reacting the active chloride with diethylamine in the presence of base (NaOH).
[VISUAL]
The activation step using thionyl chloride can be accomplished in two alternative ways:
a) by heating the m–toluic acid with thionyl chloride (SOCl₂) and
b) by reacting m–toluic acid at room temperature, with SOCl₂ in the presence of a catalytic amount of pyridine.
With regards to the yield and purity of the final product, procedure b is preferred over procedure a since the latter leads to the creation of anhydride 3 as a by-product.
[VISUAL]
+ heating

Experimental
m^-Toluic acid (0.5 g, 3.7 mmol), dry ether (0.2 cm 3 ), pyridine (2 drops), and 99.5 % SOCl₂ (0.55 cm 3 , 7.6 mmol) are stirred for 8 minutes at room temperature in loosely stoppered 5 cm 3 round–bottom flask. The reaction is performed in a fume hood; alternatively, the liberated HCl gas may be directed to an aspirator. The excess SOCl₂ is then removed at room temperature under water–aspirator vacuum (25 mmHg) and the oil residue is pipetted into a mixture of diethylamine (1.3 cm 3 , 12 mmol) in 10% NaOH (5 cm 3 ) at 0 °C. After stirring for 1 minute, the solution is extracted twice with 15 cm 3 portions of ether. The ether fractions are dried over MgSO₄ (or Na₂SO₄) and filtered, and 1 cm 3 of toluene is added to azeotropically remove any traces of both water and pyridine. The solvents are removed under vacuum in a rotary evaporator until dryness. DEET remains as a clear oil in the round–bottom flask.