Ernst Otto Beckmann – discoverer Beckmann rearrangement

Ernst Otto Beckmann – discoverer of Beckmann rearrangement

Category : Personalities
Published by : Data Research Analyst, Worldofchemicals.com

Biography & contributions

Ernst Otto Beckmann, a German chemist was born on July 04, 1853 – died on July 12, 1923. Beckmann had done some important works in chemistry filed like invented Beckmann differential thermometer and also discovered Beckmann rearrangement.

Beckmann differential thermometer


The Beckmann differential thermometer is a device used to measure small differences of temperature, but not absolute temperature values.

A Beckmann thermometer's length is usually ranges from 40-50 cm. The temperature scale in this thermometer typically covers about 5 degree centigrade and it is divided into hundredths of a degree. Beckmann thermometer's magnifier makes possible to estimate temperature changes as low as 0.001 degree centigrade.

The important feature of Beckmann's thermometer design is a reservoir at the upper end of the tube, by means of which the quantity of mercury in the bulb can be increased or decreased so that the instrument can be set to measure temperature differences at either high or low temperature values. In contrast, the range of a typical mercury-in-glass thermometer is fixed, being set by the calibration marks etched on the glass or the marks on the printed scale.

Beckmann rearrangement

Beckmann rearrangement, named after the German chemist Ernst Otto Beckmann is an acid-catalyzed rearrangement of an oxime to an amide. The Beckmann solution consists of acetic acid, hydrochloric acid and acetic anhydride, and was widely used to catalyze the rearrangement. Other acids, such as sulfuric acid or polyphosphoric acid, can also be used.

Mechanism

The Beckmann rearrangement reaction begins by protonation of the alcohol group forming a better leaving group. The R group trans to the leaving group then migrates to the nitrogen, resulting in a carbocation and the release of a water molecule. This trans [1-2]-shift allows for the prediction of the regiochemistry of this reaction. The water molecule then attacks the carbocation and after deprotonation and tautomerization results in the final amide product.

Tautomerization

Tautomerization is the process of conversion of a species formed in a reaction into a tautomer. This reaction commonly results in the formal migration of a hydrogen atom or proton, accompanied by a switch of a single bond and adjacent double bond. The concept of tautomerizations is called tautomerism. Tautomerism is a special case of structural isomerism and can play an important role in non-canonical base pairing in DNA and especially RNA molecules.

Examples of tautomeric pairs

Ketone – Enol

Amide – imidic acid

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