M Chlorobenzaldehyde

Both the olefin stereochemistry observed and the results of cross-over experiments (added m-chlorobenzaldehyde) confirm the faster rate of reversibility (to ylide and aldehyde) of cis-(34) compared to trans-(34) and indicate that this difference is greater than earlier work had suggested. Even more interesting is the observation of a synergistic effect (leading to excessively enhanced amounts of (E)-alkene) when deliberately prepared mixtures of ervthro- and threo-(33) are decomposed. The volumes of activation... 

The Claisen-Schmidt condensation of 2 -hydroxyacetophenone and different chlorinated benzaldehydes over MgO has been investigated through kinetic and FTIR spectroscopic studies. The results indicate that the position of the chlorine atom on the aromatic ring of the benzaldehyde substantially affects the rate of this reaction. In particular, the rate increases in the following order p-chlorobenzaldehyde < m-chlorobenzaldehyde < o-chlorobenzaldehyde. The difference between the meta and para-substituted benzaldehyde can be attributed to electronic effects due to the difference in the Hammett constants for these two positions. Steric effects were found to be responsible for the higher rate observed with the o-chlorobenzaldehyde. 

Additional adsorption studies were also carried out using para- and ortho-chlorobenzaldehydes (Figure 4). The results obtained with p-chlorobenzaldehyde are very similar to the ones obtained with m-chlorobenzaldehyde and were omitted from this paper for brevity. In contrast, substantial differences are observed in the spectra of adsorbed o-chlorobenzaldehyde. In particular, in this case the 1620 cm"1 band characteristic... 

The diazonium solution is added to the hot cuprous chloride solution while the latter is shaken by hand but is not cooled. After the solutions are thoroughly mixed, 840 cc. of concentrated hydrochloric acid is added, and the mixture is allowed to stand overnight. The reaction mixture is steam-distilled to separate the w-chlorobenzaldehyde, which is collected practically completely in the first 1500 cc. of distillate. The w-chlorobenzalde-hyde is removed from the aqueous distillate by extraction with two 150-cc. portions of ether, and the ethereal solution is dried with 10-15 g. of anhydrous calcium chloride. After being decanted from the drying agent, the ether is distilled, and the residual liquid is distilled under diminished pressure. The m-chlorobenzaldehyde boils at 84-86°/8 mm., io7-i09°/26 mm. (Note 5). The yield is 70-74 g. (75-79 per cent of the theoretical amormt) (Note 6). 

This procedure is adapted from the preparation described by Marvel and Schertz.3 w-Chlorophenylmethylcarbinol also has been prepared from m-chlorobenzaldehyde and methylmagnesium iodide.4-6> 6... 

The following aldehydes may be condensed in similar manner to the above procedure to give the corresponding substituted 9-benzal-fluorene of the indicated melting point. o-Tolualdehyde, m.p. 109.5° p-chlorobenzaldehyde, m.p. 149.5° m-chlorobenzaldehyde, m.p. 90.5° and m-bromobenzaldehyde, m.p. 92-93°. 

Since m-chlorobenzaldehyde is oxidized easily by atmospheric oxygen, it should be stored in a tightly corked or sealed container. 

When heated with m-chlorobenzaldehyde and triphenylphosphine in ethanol, the epoxides A and B give rise to products C, D, E, and F in the yields indicated. Much more D is formed from the trans epoxide than from the cis. Explain these observations and point out their relevance to the mechanism of the Wittig reaction. 

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