the -COOH 2 -CHO problem

[otto]

a frequently discussed issue on the hive is how to make
a benzaldehyde from the corresponding benzoic acid. especially
the conversion of trimethyl gallic acid into 3,4,5TMBA or
piperic acid into piperonal (the "black pepper route") is
a matter of interest.
to the existing routes (rosenmund-reduction of the acid chloride,
via ester-->benzyl alcohol) i would like to add one, that has
yet been overlooked (afaik). in Berichte 59 , pp 727-737, (1926),
they make 3,4,5-TMBA from the hydrazide of 3,4,5 TMbenzoic acid.
procedure is as follows:

1 g hydrazide is dissolved in 70 ml of water along with 6times the
molar amount of ammonia. to the mixture is gradually added 3times
the molar
amount of potassium ferricyanide keeping the temperature as low as
possible (ice bath).
after filtering off 10% of acylhydrazone, 56 - 59% of the aldehyd
is extracted by means of ether.

the article is very interesting, as it gives some background notes
on this topic. the hydrazide is prepared by 8 hour reflux of TMBenzoic
acid methyl ester with hydrazine hydrate.

otto

[halfapint]

With the hydrazide (USUAL PRECAUTIONS with hydrazine's delayed toxicity) dissolved in chilled aqueous ammonia, 3 moles of ferricyanide are added, filter and extract with ether. Expect I'd subject the residue of the ether extract to saturated bisulfite, to see what it does on addition of alcohol.

Wonder if the specification of the ferricyanide ion is replaceable with other cations which complex with the ammonia, e.g., many iron  salts. Nickel salts. In fact, would ferrocyanide do. And so forth. This shows I really don't know what is going on in this reaction. I didn't ask. Did I ask?
a half a pints a half a pound a half a world a half a round

[Aurelius]

does it claim to convert any hydrazide in said manner?  like say a phenyl hydrazide of a the target compound?

[otto]

hi halfapint,

the ferricyanide is used to oxidize the hydrazide. yes, to oxidize. in the reaction, nitrogen is evolved, the ferricyanide is converted into ferrocyanide. the article states that you can use other oxidants.

otto

[otto]

hi aurelius,

they have given the procedure only for hydrazides. phenylhydrazides are not mentioned. during reaction:

R-CO-N2H3 + (O) --> RCHO + N2 + H2O

two of the three hydrogens on the hydrazide-group are oxidized, the third is then remaining in the aldehyde. but this is only ottos opinion, maybee he is wrong.

otto