Phosphoric reagent

Scheme 6 shows a novel C-P bond forming reaction, in which the ligand coupling of an alkyne and a tertiary phosphine on palladium metal occurs. It was also considered very important that a C-P bond could be formed by the addition of a phosphorous reagent to unsaturated compounds. 

These in situ oxidations, followed by condensation with a phosphorous reagent, are normally not possible on ketones, because of their lack of reactivity with stabilized phosphoranes and phosphonate anions. Nevertheless, one-pot condensation with ketones can occur in very favourable... 

Other organo-phosphorous reagents are based on the mixed carboxylic-phosphoric or phosphinic anhydrides. Initially used to convert carboxylic acids into acyl azides, DPPA 12 has been introduced as a one-pot coupling reagent for peptide chemistry (32), and it was adapted later to solid-phase chemistry (81). The driving force of these reactions is the formation of the phosphoric or phosphinic acids and their salts. Later DPP-Cl 49 (82) and FDPP 50 were introduced. FDPP 50 has been used successfully in macro cyclizations (83). Examples of... 

Activating groups other than acid can be used to promote cyclization of these substrates. Phosphorous reagents like PCI5, POCI3, and PhaP Ch have been used to promote the cyclization. ... 

An anion on the p-keto phosphonate is formed, thanks to the use of excess of basic phosphorous reagent. This miion reacts intramolecularly with the ketone. 

Usually, phenols and alkyl alcohols are sufficiently nucleophilic for the reaction with the trivalent phosphorous reagent. In some cases, the use of alcoholates may be advantageous. Alternatively, Me Si may serve as a leaving group (Scheme 2.96)... 

Hanessian and coworkers reported an improved variation of this approach. They were able to prepare the chiral phosphorous reagent 95. Upon deprotonation to form the ylide and exposure to ketone 96, the desired product 97 could be formed in good optical purity. 

The most widely studied example is the SCCG of poly(4-oxybenoate), FOB, also called poly(4-hydroxybenzoic acid).PHB. Since the abbreviation PHB is also used for poly(/ -hydroxybutyric acid), this abbreviation is avoided in this text. Early attempts to polymerize 4-hydroxybenzoic acid, 4-HBA are discussed in Chap. 2. In the twentieth century several derivatives of 4-HBA were successfully used as monomers (see Formula 13.4), but polymerization of 4-HBA itself was also conducted in solution by means of dehydration agents, such as trifluoroacetic acid [60], thionyl chloride [61], poly(ethyl phosphate) plus imidazole [62], and various other phosphorous reagents [63]. However, these polycondensations were typically conducted at temperatures <150 °C and yielded oligomers. More than 90 % of all publications dealing with synthesis and characterization of POB are based on polycondensations of 4-acetoxybenzoic acid, 4-ABA, at temperatures around or above 300 °C. A first attempt to polymerize 4-ABA in bulk at temperatures up to 300 °C was published in 1959 [64]. The resulting polyester was described as intractable and thermally unstable above 350 °C. 

Phosphorus pentoxide. This is an extremely efficient reagent and is rapid in its reaction. Phosphoric oxide is difficult to handle, channels badly, is expensive, and tends to form a syrupy coating on its surface after a little use. A preliminary drying with anhydrous magnesium... 

Sonnenschein s reagent (alkaloid detection) a nitric acid solution of ammonium molybdate is treated with phosphoric acid. The precipitate so produced is washed and boiled with aqua regia... 

Aniline — Diphenylamine — Phosphoric Acid Reagent Reaction (according to [16])... 

To detect glycosides heat the chromatograms to 130—150°C for 15 min. Blue-grey zones are produced (detection limit prunasin 0.3—0.5 pg [18]). Flavonoids are better detected with a modified reagent of the following composition phosphoric acid (85%) — acetic acid — aniline — diphenylamine (20 ml - -100 ml + 5 ml + 5 g). 

Note The detection limit for aryl- and thioglucosides is 100 — 200 ng substance per chromatogram zone [2]. Reduction of the proportion of phosphoric acid in the reagent leads to loss of sensitivity [2]. 

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