Synthesis of 7.7-Dichlorobicyclo [4.1.0]Heptane – Phase Transfer Catalysis

1473 Words Sep 29th, 2008 6 Pages

The preparation of 7.7-dichlorobicyclo [4.1.0]heptane which is also known as 7,7-dichloronorcarane was done by reacting cyclohexene , chloroform and a base( 50% aqueous sodium hydroxide) with benzyl triethylammonium chloride. The latter being a water soluble phase transfer catalyst (PTC).reaction was performed at room temperature and was distilled at atmospheric pressure. The mechanism of action of the above mentioned PTC is described in the text along with the mechanism for the addition of a dichlorocarbene. The percentage yield obtained was 38.80%. This is considerably low due to an unfortunate spillage of the product at the stage of semi- micro distillation.

Phase transfer catalysts (PCT) are used to
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This is important since an accumulation of water can result in undesired reactions between chloroform or carbine with water. These reactions (a and b) are illustrated below.3 Deprotonation of chloroform results in the formation of a trichloromethide anion.2 .It follows that this anion then slowly releases a chloride group to form the dichlorocarbene (mechanism 2). Here the PTC can also transport the chloride ions back to the aqueous phase via a base-induced β-elimination. The carbine then attacks the double bond of cyclohexene to finally produce 7.7-dichlorobicyclo [4.1.0]heptane.

An Infrared and Gas chromatography analysis was done on the product for identification purposes. The IR spectra were analyzed and the C-Cl bond was identified in the region 580-785 cm-1. The sp3 hybridized C-H bonds were identified in the region just below 3000cm-1.CH2 bending and stretching peaks were identified in the region 1250-1465cm-1. The gas chromatogram had two peaks and this could be due to the possibility of obtaining an impure product. These spectra are attached at the end of this report.

The synthesis of 7.7-dichlorobicyclo [4.1.0]heptane achieved in a reasonable duration of time with the aid of the phase transfer catalyst, benzyl triethylammonium chloride which facilitated the generation of the dichlorocabene which reacted with hexane to produce the desired product.

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