Additions of water, hydroxide ions, alcohols and alkoxide ions to carbonyl and azomethine bonds

Abstract

In this review are discussed equilibria involved in nucleophilic additions of H 2 O, HO -, ROH, and RO -(where R is an alkyl) to compounds containing carbonyl and azomethine bonds. These reactions result in a formation of covalent bonds between the heteroatom of the nucleophile and the carbon of the carbonyl double bond. After a brief summary of reactions resulting in additions to aliphatic carbonyl compounds, attention is paid to additions to benzaldehydes and formyl aromatic heterocycles. Equilibria involving additions to pyridoxal and some related compounds are dealt with in some detail. Discussion of additions of stated nucleophiles to azomethine bonds is practically restricted to additions to C=N bonds in heterocyclic rings. The reactivity of nucleophiles in such additions depends on the number of heteroatoms (in particular nitrogen) in the attacked ring, as well as on the number and position of substituents in such rings. In polynuclear compounds the reactivity depends on the number and kind of annelled rings, on the number and mutual position of heteroatoms and on the kind, number and position of substituents. In particular additions to pyrimidines, quinazolines, 1,2,4-and 1,3,5-triazines, pteridines and other heterocycles with four nitrogens, as well as 8-azapurines are mentioned.

PTFE supported gold nanoparticles as photocatalysts for oxidative esterification of aldehydes

“…The reported hemiacetal formation equilibria for substituted benzaldehydes in the presence of methanoate CH 3 O À has a large positive Hammett r value (r Hemi = 3.20). 50,51 In the absence of base, the reported hemiacetal formation equilibrium Hammett plot has a much lower r value (r Hemi = 2.00) close to our measured value. These two positive Hammett r values strongly suggest that the rate determining step of the reaction referred to the hemiacetalisation step.…”

Electrochemical Determination of HIV Drug Abacavir Based on Its Reduction

“…Such behavior indicates that ∼40% of I is in aqueous solutions present in hydrated form. A similar hydration of an azomethine bond has been reported for pyrimidine derivatives . In the ability of covalent addition of water, I may differ from purine bases, for which no covalent hydration has been reported …”

“…The decrease of the limiting current of III between pH 1 and 4 (Figure A) indicates that less than 20% of this compound is present in aqueous solutions in covalently hydrated form. It is not surprising that such a low degree of hydration has so far escaped attention . Covalent hydration of this compound most probably involves a nucleophilic addition of water to a CN bond in the pyrimidine ring.…”

Strong Covalent Hydration of Terephthalaldehyde

“…Covalent addition of water to aliphatic carbonyl compounds has been investigated in considerable detail. − With some of the aldehydes, the hydration is so strong that they are present in aqueous solutions in more than 99% in the hydrated form. Strong covalent hydration has also been observed in aqueous solutions of aldehydes, bearing a formyl group on a π-deficient aromatic ring. − On the other hand, aldehydes where the formyl group is located on a benzenoid aromatic or π-excessive heteroaromatic ring have been for a long time assumed to remain in aqueous solutions practically unhydrated . Hence, for example, benzaldehyde as well as 3- and 4-chlorobenzaldehydes are less than 1% hydrated .…”

“…This was attributed to a considerable resonance stabilization of the unhydrated form. For most substituted benzaldehydes the nucleophilic additions were observed only in the presence of stronger nucleophiles, such as hydroxide or alkoxide ions. ,− …”