Formaldehyde as an oxidation product of chlorophyll extracts

Of recent years the action on carbon dioxide of chlorophyll in vitro has assumed some importance as possibly throwing light on the nature of the photo-synthetic process of green plants. Thus Usher and Priestley have stated that films of extracted chlorophyll in the presence of moist air and carbon dioxide produce formaldehyde and hydrogen peroxide under the influence of light. The earlier work of these authors has been adversely commented upon by several writers, notably by Ewart, to whose criticisms Usher and Priestley have replied with a number of additional experiments and arguments, referring also to the work of Schryver, subsequent to that of Ewart, as affording strong confirmation of their views as far as the synthesis of the aldehyde is concerned. The facts set forth in the present paper came to light during an attempt to confirm and extend the observations of Usher and Priestley and of Schryver. Grass was extracted with alcohol, usually in the cold and in the presence of calcium carbonate. In some experiments the alcoholic liquid was evaporated to dryness under reduced pressure and the residue extracted with ether; in others a solution of chlorophyll in light petroleum was obtained by shaking the alcoholic solution with that liquid. The method of experiment was based upon that described by Schryver, the ether or petroleum extract being allowed to evaporate on glass plates and exposed to light under the various conditions to be mentioned below. As was the case in the later experiments of Usher and Priestley themselves, the test which has been relied upon for the detection of formaldehyde is the very delicate one devised by Schryver, who has found that the reaction is not given by such other members of the series as have been examined up to the present. It has been assumed in the course of these experiments, as in the work of the investigators already mentioned, that the aldehyde produced is formaldehyde, but it is very important that the possibility of the observed effects being due to some other aldehyde or to a mixture of aldehydes should be borne in mind. This point still requires investigation.