Gertrude Maud Robinson

Gertrude Maud Robinson ( Walsh; 1886–1954) was an influential British organic chemist most famous for her work on plant pigments; the Piloty-Robinson Pyrrole Synthesis, which is named for her; her syntheses of fatty acids; and her synthesis of δ-hexenolactone, the first synthetic molecule with the character of penicillin. Robinson was born on 6 February 1886 in Winsford, Cheshire and died of a heart attack on 1 March 1954, in Oxfordshire, aged 68. before briefly going to the St. Andrews in Scotland and University College in London. She worked on the syntheses of saturated and unsaturated fatty acids and was the first to synthesize oleic acid and lactarinic acid. Her methods led to her synthesis of fatty acids with the greatest molecular weights of the time (specifically, tricontanoic and 13-oxodotetracontanoic acids).

After moving to the University of Oxford, Gertrude Robinson began studying plant pigments and published extensively on anthocyanins with her husband. She was the first to observe that the color of a plant’s pigment was not related to the pH of its sap The Robinsons found that, at different ratios of anthocyanins to copigments, the copigments had different effects and they postulated that this was due to the copigments breaking up the anthocyanin complexes, which they observed when they were in solution together. (The Robinsons, who lacked a machine with which to extract pigments, instead would cover the relevant plants with boards and then drive back and forth over them.)

Leucoanthocyanins The Robinsons investigated the structure of leucoanthocyanins, colorless molecules that generate anthocyanidins and are present in most plants. Rosenheim simultaneously discovered leucoanthocyanins and he coined the term. Leucoanthocyanins occur in more locations (wood, bark, nutshells, flowers, fruits) than normal anthocyanins.

The mechanism for the Piloty-Robinson Pyrrole Synthesis suggested by Gertrude and Robert Robinson.

There are, however, a few problems with some syntheses. The Piloty-Robinson reaction competes with the formation of pyrazoline when the reactant is an aliphatic azine derived from a ketone. Also, under high temperatures and highly acidic solutions, azines derived from aldehydes are not stable. This prevents the formation of 2,5-disubstituted pyrroles (where R=H) using this method.

Modern Uses While the pyrroles produced by the Piloty-Robinson Synthesis are often very useful, the reaction itself is not always favorable because it requires high temperatures and long reaction times in addition to the problems mentioned above, the yield is often low or moderate. Modern methods have alleviated some of these concerns.

Microwave Irradiation Microwave radiation decreases the time necessary for the reaction from around 3 days to 30-60 min. It can also affect the yield.

Fischer Indole Mechanism The Robinsons disproved many of the prevailing theories about the Fischer Indole Mechanism by showing that the reaction went unperturbed in the presence of other aromatic amines such as p-toluidine. This is the mechanism they suggested (where hydrogen shifts may also be interpreted as hydrogen exchanges in acid).

Gertrude Robinson's synthesis of n-triacontanoic acid. The Robinsons showed that this was in fact 6-ketostearic acid by doing a Beckmann Transformation on the oxime of lactarinic acid. They then synthesized 6-ketostearic acid via a reaction of ethyl sodio-2-acetyl-n-tridecoate and 5-carbethoxyvaleryl chloride and then hydrolysis to prove the structure of lactarinic acid.