Naphthaldehyde, reduction

Most of the methods for preparation of /3-naphthaldehyde have been given previously.2 A recent procedure describes the preparation of /3-naphthaldehyde from 2-bromomethylnaphthalene and hexamethylenetetramine in boiling acetic acid.3 The method of reduction of nitriles by stannous chloride was discovered by Stephen.4... 

Several explanations can be offered for the reactivity of the naph-thaldehydes. The reaction could be taking place with (/) the 77,77 triplet (2) the n,ir triplet, which could be formed on the way to, or in some cases, be in thermal equilibrium with, the 77,77 triplet or (5) the h,tt singlet, formed either directly upon absorption or on the way to the triplet. It is not possible, at this time, to definitely rule out any of these possibilities. However, there is evidence indicating that, in the case of naphthaldehyde, the 77,77 triplet can be the reactive state involved, since the reduction is sensitized by triplet-triplet transfer with sensitizers having a triplet energy such that only this state is activated.47... 

Naphthaldehyde has been made from a-naphthonitrile by reduction with stannous chloride, and from naphthalene by the action of aluminum chloride, hydrogen cyanide, and hydrochloric acid. The best preparation is the Sommelet reaction from a-chloro- or a-bromomethylnaphthalene and hexamethylenetetramine in aqueous alcohol is.is. .is.w or glacial acetic acid. This method has been improved in the present procedure by the use of 50% acetic acid as solvent. 

Neyroz et al. [97] have covalently linked 2NpOH to phos-phatidylethanolamine moiety by the Schiff-base formation between the NH2 of the phospholipid and the aldehyde moiety of 2-hydroxy-1-naphthaldehyde, followed by selective reduction of the imine to obtain a stable secondary amine. This fluorescent phospholipid easily incorporates into DML vesicle membrane and exhibits the typical behavior of ESPT probes. The emission spectrum of this probe inserted in the liposome is similar to that in ethanol medium and is affected by acetate used as a proton acceptor. 

Aldehydes are easily hydrogenated to alcohols but ketones are more difficult to reduce because of steric hindrance. Hydrogenolysis is a problem with the catalytic reduction of carbonyls, particularly when linked to aromatic systems. Pd and H2 reduce alkenes faster than carbonyls. Metal catalyst Pt is commonly used for the reduction of carbonyls. For example, the Adams catalyst (Pt02) reduces 2-naphthaldehyde (6.31) to 6.32 in 80% when used with FeCls as a promoter. When excess of the promoter is used the product is 2-methylnaphthalene (6.33), which is also obtained by the reduction of 6.31 with Pd on BaS04 and H2. 

Nitriles may be converted to their imino chloride salts by the action of dry hydrogen chloride in ether. These intermediates ate reduced by anhydrous stannous chloride to stannic aldimonium chlorides, which on hydrolysis yield aldehydes. Chloroform may be added to facilitate the solution of the nitrile. The quality of the stannous chloride catalyst is important the preparation of an active and dependable form has been described. The yields are usually high for many aromatic nitriles, as in the preparation of /3-naphthaldehyde (95%). The reaction has also been employed in the heterocyclic series, as in the synthesis of 4-methyl-thiazole-5-aldehyde (40%). The reduction of the cyano group in the... 

Naphthaldehyde has been prepared from /3-chloro- or bromomethylnaphthalene by use of hexamethylenetetramine, or by oxidation with lead nitrate from /3-naphthoic acid by distillation with calcium formate, or by reduction with sodium amalgam in boric acid solution from /3-naphthylcarbinol by oxidation with chromic acid and from (3-naphthylglyoxylic acid by saponification, heating with aniline, and hydrolysis of the anil." It has been prepared from j8-naphthylmagnesium bromide and ethoxymethyleneaniline or orthoformic ester, ... 

This reagent has also been converted to the dithioacid with carbon disulfide and this acid converted to 3-naphthaldehyde by way of its semicarbazone. (3-Naphthaldehyde has been made by the reduction of /3-naphthonitrile according to Stephen and by the reduction of 3-naphthoyl chloride according to Rosenmund." The procedure described is based on the method developed by Rosenmund and applied by him and others to... 

Reaction of nitriles with dry hydrogen chloride in anhydrous ether or in an ether-chloroform mixture affords imidoyl chlprides which are reduced by stannous chloride to products that afford aldehydes on hydrolysis. The method seems to be generally applicable only to aromatic and heterocyclic aldehydes the activity of the stannous chloride used for the reduction seems to be the most important factor in the reaction.580 2-Naphthaldehyde has been synthesized580 in 95% yield by this method, and 4-methyl-5-thiazolecarbaldehyde in 40% yield.581... 

Tin metal is used sparingly as a reducing metal in modem organic synthesis, which contrasts with tin derivatives such as tributytin hydride, which are common. Aldehydes, for example, are readily reduced with tributyltin hydride (Bu3SnH) in aqueous media. An example is the reduction of 2-naphthaldehyde to the alcohol (396) in 93% yield in refluxing methanol.5l5 when this reaction was done in water, and 85% yield of 396 was obtained. 

Several other aromatic aldehydes form more stable SchifF bases which have Found some use as amino-protecting groups. These SchifF bases are derived from salicylaldehyde (50) , 5-chlorosalicyl-aldehyde (51) , 2-hydroxy-1-naphthaldehyde (52) i 1 7 nd -methoxysalicylaldehyde (53) . These SchifF bases could be cleaved by treatment with acid but they are resistant toward reductive cleavage by catalytic hydrogenadon (contrary to the benzylidene... 

Rosenmund Reaction. A catalyst poison prepared from quinoline and sulfur is useful for controlling the reaction of p-naphthoyl chloride (19) with hydrogen gas and palladium on barium sulfate catalyst. If control of the reaction is not maintained by catalyst poisoning to reduce activity, further reduction beyond the desired /3-naphthaldehyde product (20) is often observed (eq 13). ... 

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