Sciencemadness Discussion Board

Acid to aldehyde w/o hydrides?

Intergalactic_Captain - 16-7-2008 at 07:43

Heres a simple question - How would one go about reducing a substituted benzoic acid to the corresponding benzaldehyde without the use of either a 1-step hindered hydride (ie. DIBAL-H), or a 2-step reduction/oxidation (ie LAH ->PCC)? Catalytic hydrogenation is the only other option I've found, but that's basically not an option at the current time (very high pressure, low yeilds). Hydrides are out due to aquisition issues (land of the free my ass).

Normally I'd sit on crossfire for a day or two before asking something like this, but the server my school uses no longer allows off-campus access on our account. I'm gonna give scifinder a shot later, but we've only got 6 licenses for 17000 students so very rarely can one actually use it.

Klute - 16-7-2008 at 08:07

I remeber one what which consist of making the benzonitrile with urea and sulfamic acid (GB2151626) , then hydrogenating the nitrile to the aldehyde with copper-treat Raney nickel (US4500721), or CTH with Raney nickel and formic acid (US4383949, Van Es, Staskun, J. Chem. Soc., 1965, 5775 ).

Credit goes to Antoncho from the former Hive for retreiving most of this info.

EDIT: there are several electrochemical methods too, used in the industry, some including protecting the aldehyde as forme dby it's bisulfite adduct.

[Edited on 16-7-2008 by Klute]

Intergalactic_Captain - 16-7-2008 at 08:19

The nitrile is definitely possible with my resources...I've actually been searching for an excuse to try out the SOCl2-free dehydration for a while, this one might actually be worth the trouble. Would you happen to have a non-patent reference on the hydrogenations? I'm going to check them out now, but in general I've found patents are too vague to be of any practical value.

EDIT - I meant SOCl2-free dehydration for amide->nitrile if anyone misses it... It's been in the back of my mind for a while, I had to dig up some literature to prove to a professor that it was possible last year to get credit for an exam question.

EDIT 2 - That first patent is exactly what I was looking for...Now to either find some sulphamic acid or figure a way to do without it.

[Edited on 7-16-08 by Intergalactic_Captain]

[Edited on 7-16-08 by Intergalactic_Captain]

sonogashira - 16-7-2008 at 09:31

Perhaps you're already aware of this:

Stephen reduction of nitriles to benzaldehydes...

Attachment: Substituted Benzaldehydes via Stephen Reduction.pdf (254kB)
This file has been downloaded 1337 times

Intergalactic_Captain - 16-7-2008 at 10:57

Was not aware of that one, but thanks...I've got to look through my synthetic o-chem notes though, it looks pretty familiar. Looks like this project's finally got some legs. Step one is outlined in US patent 4501920 if anyone's interested, 20 lbs of sumac leaves are currently drying.

Klute - 16-7-2008 at 13:13

Sulfamic acid is commonly found at swimming pool stores AFAIK.

Intergalactic_Captain - 16-7-2008 at 13:35

Yeah, I realized that after I posted... I've had a hard time finding it in the past, but I just found out my home depot carries it for $5/lb - It's listed as a grout and masonry cleaner, I'm assuming it's reasonably pure as it's labeled "Sulfamic Acid Cleaner." Hopefully grab some tomorrow to find out, it's not listed in the NIH database.

flyingbanana - 28-7-2008 at 20:55

if you feel like playing with some cyanide salts...Riessert aldehyde synthesis

carboxylic acid -> acyl chloride, react acyl chloride with cyanide salt and quinoline followed by hydrolysis

SecretSquirrel - 28-7-2008 at 23:50

If you would like to avoid the use of cyanides there is also the Rosenmund reduction. First you turn your acid into acyl chloride (w/PCl5 or some other reagent) and then reduce it to an aldehyde.

Rosenmund reduction

not_important - 29-7-2008 at 01:05

The old school way would be to mix divalent salts of the acid and formic acid, with the format in many-fold excess, then heat to 300-400 C. Calcium, barium, and Mn(2+) salts were most commonly used, sometimes tri- or quad- valent salts were used such as the thorium salts. Yields generally are low, with side products to annoy you as well.

The electrolytic methods can give good yields, although in some cases the benzyl alcohol is the main product and over-reduction can lead to the substituted toluene. However these reductions are somewhat of an art, with a number of runs being needed to optimize conditions.

S.C. Wack - 29-7-2008 at 03:25

One of the easier methods without something like LAH or hydrogenation with a catalyst would be less direct as well, making the ester, reduction using a borohydride or sodium, and oxidation. Or the alcohol directly from the acid with NaBH4/iodine in THF (supposedly). Not within the narrow parameters but oh well.

[Edited on 29-7-2008 by S.C. Wack]

Ozone - 29-7-2008 at 16:27

How about a Swern oxidation (sorry I'm on this oxalyl chloride trip right now) from the alcohol?

I with you on the Scifinder...we have 5 seats for 35,000:(.

Cheers,

O3

S.C. Wack - 10-8-2008 at 00:28

Ah, I forgot about this one, buried in my handwritten notes. In JCS 84 (1943) 0.1 mole benzoic acid, 0.11 mole HCOOH, and 0.5 g. TiO2 was placed in a 1"x15" glass tube which was then sealed. I think (note gets fuzzy here) that this tube was then placed in a larger steel tube for safety, which was in a larger steel tube filled with solder. Maybe the empty inner steel tube had been placed in the larger while solder was molten, and left to cool before addition of the glass tube, or not. But I do have written down that the whole was then heated to 260C over a 3 hour period, and maintained there for another 2 hours. The product was isolated by extraction with ether, and acid removed by washing the ether with NaOH.

Benzoic acid only gave a 37% yield of benzaldehyde, but there was a 92% yield of salicylaldehyde.

S.C. Wack - 13-12-2008 at 19:27

Better than handwritten notes:

Attachment: jcs_84_1943.pdf (302kB)
This file has been downloaded 1378 times

Sandmeyer - 20-12-2008 at 02:33

You can reduce acyl halides to aldehydes with Pd/C, classical reaction is called Rosemund reduction and it uses poisoned catalyst but more recent developments have been made where plain Pd/C (5%) is used, in excellent yields. I don't have refs since I'm away from the litterature during the holidays, I can post later if you're interested in this reduction.

Nicodem - 20-12-2008 at 02:58

I'm also fairly sure you could use 5% Pd-C, instead of the classical Pd-BaSO4, if you poison it with thiophene, quinoline or pyridine.
However, this is the only relevant reference that I could find at the moment:
Quote:
The synthesis of aldehydes by means of a modified Rosenmund reduction of acid chlorides.
Peters, J. A.; Van Bekkum, H.
Recueil des Travaux Chimiques des Pays-Bas, 100 (1981) 21-24.

Abstract: Aliph. as well as arom. acid chlorides were reduced smoothly to aldehydes at room temp. and atm. hydrogenation over Pd/C with acetone or EtOAc as solvent and ethyldiisopropylamine as HCl acceptor. No over-redn. nor redn. of arom. rings, of nitro and chloro substituents in benzoyl chlorides, or double bonds in cinnamoyl chlorides, was obsd. The high selectivity was the result of selective adsorption of the acid chloride on the catalyst (with respect to the aldehyde) and partial poisoning of the catalyst surface by co-adsorption of ethyldiisopropylamine and its hydrochloride.

Edit: Apparently using poisoned Pd-C is more common than I thought. It is even described in an Org. Syn. entry, the one that SecretSquirrel posted upthread.

[Edited on 20/12/2008 by Nicodem]

grind - 20-12-2008 at 03:32

A rather clean conversion of acids to aldehydes (unfortunately with hydrides) takes place as follows:
The acyl chloride reacts with P(OEt)3, this is reduced with NaBH4. References are in the Alfa chemicals catalogue, which I don´t have at hands in the moment.

Other possibility:
Bouveault-Blanc reduction of an ester (of the acid) yields the alcohol, which can be oxidized to the corresponding aldehyde. No need for hydrides, but for sodium metal.

Klute - 22-12-2008 at 08:21

Wouldn't the ester give an acyloine condensation in presence of sodium?