Lobry de Bruyn-Van Ekenstein

Chemists usually learn about reactions according to fiinctional groups for example, How can I make an aldehyde and what reactions are known for aldehydes " This is clearly not a very good starting point for classifying reactions. The poor state of affairs in the definition of reaction types is further quite vividly illustrated by the fact that many chemical reactions are identified by being named after their inventor Diels-Alder reaction, Michael addition, Lobry-de Bruyn-van Ekenstein rear-... 

The synthesis of D-psicose as a colorless sirup ([< ]% + 3.1° in water) by Steiger and Reichstein13 may be regarded as the first authentic preparation of this ketohexose. The Kiliani-Fischer cyanohydrin synthesis furnished D-allonic lactone (VII) from D-ribose. This lactone, on reduction with sodium amalgam, gave D-allose (VIII) which was transformed into D-psicose (I) by refluxing with pyridine. Pyridine had been introduced into the Lobry de Bruyn-Van Ekenstein reaction by Fischer, Danilov and their coworkers.13 ... 

Scheme 5.2 Lobry de Bruyn-van Ekenstein transformation of D-glucose.

MPa H2. To suppress the isomerization of D-glucose to D-mannose and D-fructose (Lobry de Bruyn-van Ekenstein transformation) (Scheme 5.2) and the Cannizzaro reaction, which were both promoted in an alkaline medium, the pH value was maintained between 5.5 and 6.5. Under the conditions that were optimized to minimize the side reactions, the formation of gluconic acid and mannitol was reduced to less than 1% each at 99.5-99.6% conversion, while with a normal nonpromoted Raney Ni 1.5-2.1% of gluconic acid and 1.3-1.9% of mannitol were formed at 99.5-99.7% conversion. 

Reactions with bases in basic medium, reducing sugars undergo isomerization reactions through enedioi intermediates (Lobry De Bruyn-Van Ekenstein reaction) so glucose is partially converted to fructose and mannose a number of by-products is also produced. 

Lobry de Bruyn-van Ekenstein transformation. Isomerization of carbohydrates in alkaline media, considered to embrace both epimerization of aldoses and ketoses and aldose-ke-tose interconversion. 

Endiols (4.80) can isomerize into other saccharides in the Lobry de Bruyn-van Ekenstein rearrangement. Thus, D-glucose (5.4) can isomerize into mannose (5.81) and fructose, (5.1) accompanied by a small amount of D-psicose (5.83). Alkaline medium provides isomerization to disaccharides, which turn from aldoses into ketoses, as shown for lactose (5.7b) isomerized to lactulose (5.84). 

This reaction is related to the Lobry de Bruyn-van Ekenstein transformation of aldoses involving the rearrangement of A-alkylamino-D-glucopyranosides into 1-alkylamino-l-deoxy-D-fructoses. ... 

This reaction was first reported by Lobry de Bruyn in 1895, and explored extensively by Lobry de Bruyn and Alberda van Ekenstein. It is the reciprocal interconversion of carbohydrates into their isomers in an alkaline solution through the enediolic intermediate. The name of reaction given here is probably the only one time the full name of the people who discovered such reaction. It is known as the Lobry de Bruyn-Alberda van Ekenstein rearrangement, Lobry de Bruyn-Alberda van Ekenstein transformation, Lobry de Bruyn-Albreda van Ekenstein C-2 epimerization, or Lobry de Bruyn-van Ekenstein transformation. ... 

By heating of foodstuffs, aldoses and amino acids form N-glycosides, which lead to Amadori products by an Amadori rearrangement (Mario Amadori (1886-1941), Italian chemist). The mechanism is analogous to that of the Lobry de Bruyn-van Ekenstein rearrangement (Cornehs Adriaan Lobry van Troosten-burg de Bruyn (1857-1904) and Willem Alberda van Ekenstein (1858-1937) were chemists from the Netherlands). 

The former base-catalyzed aldose-ketose isomerization is named the Lobry de Bruyn-van Ekenstein transformation (Scheme 6.25). Deprotonation of the a-carbonyl carbon of aldose (glucose) requires a base, and results in the form of a series of enolate intermediates. Solid bases such as cation-exchanged zeolites and Mg-Al HT catalyze glucose isomerization in water [176-178]. 

Lobry de Bruyn-van Ekenstein Transformation Loftier (see Hofmann-Loffler-Freytag Reaction)... 

Lactulose is found in heated milk products. It is a little sweeter and clearly more soluble than lactose. For example, condensed milk contains up to 1% of lactulose, corresponding to an isomerization of ca. 10% of the lactose present. The formation proceeds via the Lobry de Bruyn-van Ekenstein rearrangement (cf. 4.2.4.3.2) or via SchiffhasQ. Traces of epilactose (4-0-P-D-glacto-... 

---