I have tried several times reducing p-aminobenzoic acid with sodium borohydride and even LiAlH4, but all reaction failed. This is not simple reaction for the above said product synthesis since the cost of p-aminobenzyl alcohol is very high.
1) check whether your LAH is active 2)your solvent normally THF should be supper dray 3) you need excess amount of LAH since you have some acidic hydrogens
You may be losing much of your desired product in the work-up step. Your product is very polar and I would assume you are losing much of it with the lithium salts that form after work-up. I reduced the acids of amino acids and my yields were never very good. I used a base hydrolysis to get rid of excess LAH and the lithium salts were easily removed via vacuum filtration but beware of their horrific odor! Have you tried reducing the ester instead of the acid with LAH?
I agree that the THF has to be dry and excess LAH needs to be used. As far as I'm aware, sodium borohydride isn't going to reduce the carboxylic acid. Just be careful when you are working-up the reaction with LAH. Violent reaction with water if added too fast.
I have tried with reducing ester instead of the acid with LAH but again reaction failed. I had not used excess LAH coz of fear of having violent reaction with water of remaining LAH. May be I will have to use excess LAH and be careful during work up procedure.
Instead Can I start with reducing p-nitrobenzoic acid to p-nitrobenzyl alcohol and then reduction to p-aminobenzyl alcohol by Stannous chloride/HCl.
It may be worthwhile to try supported Pd catalysts, for the selective reduction of nitro groups to amine in the presence of other reducible substituents on the aromatic nucleus.
try p-aminobenzaldehyde. Its polymeric form in acidic media can give low concentrations of aldehyde which can be reduced
as i think it is not difficult, use dry DCM and at least 2 -3 eq and do it at 0C add smol portion every 2-3 mint after complet leave it stirring at r t 2-3 h then add dw and extruct the DCM & wash it with NaHCO3 to be sure no acid in organic layer
I agreed with Roman Voloshchuk. answer. May I get elaborate answer or any full procedure to proceed with.
Here you can find a description on the preparation of p-aminobenzaldehyde (http://orgsyn.org/orgsyn/pdfs/CV4P0031.pdf). Reduction of the aldehyde with NaBH4 is easier and cleaner than LAH reduction of an acid (derivative). If you stick to the p-aminobenzoic acid, it is better to convert it first to an ester, then reduce with LAH.
by hydrogenation of p-amino-acetophenone in the presence of Cu/Al2O3
Try reduction of p-Nitrobenzyl alcohol (Sigma N6251); even simple Zn+HCl can do it
Rajesh Singh, there are some data on reduction (Tetrahedron Letters 2006 p.5261, supplementary data; Organic Preparations and Procedures International, 2000 , p. 596) but they are based on sodium tetrahydroborate and hence the odds are that they were using free form of p-aminobenzaldehyde. If you can get some polymeric sample (which is not very common), you can try several procedures by yourself (in situ hydrolysis and reduction). You can also consider functionalizing NH2 group first if it's in your planes.
Dear Rajesh,,
Try to react p-aminobenzoic acid with Ethyl-Chloroformate to prepare mixed anhydride, then reduce with Sodium borohydride,
Esterification of p-aminobenzoic acid and reduction with LiAlH4/H2O
Dear rajesh.
There are two things you need to do before reduction. Esterification of acid to methyl ester followed by protection of amine with Boc-anhydride vice versa., and reduce using Sodium borohydride in THF followed by methanol addirion should works.
Simply use NaBH4/Charcoal in H2O-THF (1:0.5 mL) and stirred 50–60 C for 2-3 h. Ref. Synthetic Communicationsw, 36: 2699–2704, 2006. It worked best for me to make p-aminobenzyl alcohol from p-nitrobenzyl alcohol.
you have to synthesis of methyl 4-amino benzyl acetate through thionyl chloride with methanol -5 to room temperature 5 hrs. then try with sodium borohydride (or) LAH in THF at 0 to rt or -78
Dear rajesh , reduction of acid to alochol with borane dms give good result
Dear Rajesh,
The reduction of p-amino benzoic acid(PABA) by LiAlH4 will produce the alcohol. However its not possible to reduce the PABA by sodium borohydride. As an alternative you can try p-nitro benzoic acid and convert it into methyl ester by refluxing in SOCL2/methanol system. Reduce the p-nitrobenzoic acid methyl ester by NaBH4 in methanol/THF system at reflux. The yield is promising, and you get p-nitro benzyl alcohol (PNBA). Once you get PNBA you can reduce the nitro group by H2/Pd /methanol system. You can also try charcoal/NaBH4 system. I have performed both these reactions but in good amount(5gms) i have performed it in the H2/Pd/methanol system as the PNBA is highly soluble in methanol. Hope it helps.Good luck
Either better try to prepare and reduce the ester or use borane.SMe2
You can also try mixture of NaBH4 & iodine.it insitu produce BH3 which effective for reduction of acid group.
u can also try this reaction using BH3 b'coz its a chemoselective reagent for reducing acids to alcohol.
- Badges
- Science topic
- Similar topics
- Chemistry