Sciencemadness Discussion Board

BHT Synthesis

UnintentionalChaos - 25-11-2012 at 16:24

I feel like this belongs in beginnings...

Has anyone seen a lab scale prep of BHT (2,6-di-tert-butyl-4-methylphenol) anywhere?

I have some p-cresol and I'm looking to alkylate it with t-BuOH and sulfuric acid catalyst.

I found this, but am understandably a bit doubtful about the source (unreferenced). http://www.iitk.ac.in/chm/CHM101/node55.html

I am seeing a prep of 2,5-di-tert-butyl-1,4-dimethoxybenzene which is apparently from a newer edition of Fieser than our library has. http://chemistry.mercer.edu/orgchem/Friedels12.pdf

It looks like the first prep is just a modification of the Fieser procedure with a different substrate. I might resort to this, but I'd prefer a published prep specific to BHT.

Any help would be appreciated.

chemrox - 25-11-2012 at 23:40

Have you tried the unpublished lab procedure? I wouldn't worry about the rearrangement...you are already at the higher entropy end with t-BuOH ... btw is this the anti-oxidant BHT of commerce? Are you doing the synth for practice? Have you tried any of the CAS databases like scifinder?

UnintentionalChaos - 26-11-2012 at 07:53

Quote: Originally posted by chemrox  
Have you tried the unpublished lab procedure? I wouldn't worry about the rearrangement...you are already at the higher entropy end with t-BuOH ... btw is this the anti-oxidant BHT of commerce? Are you doing the synth for practice? Have you tried any of the CAS databases like scifinder?


This is indeed the antioxidant of commerce. I only need a small amount for stabilizing ethers, and while I could buy it, this seems much more interesting. Typically, the prep is done with isobutylene, but that's a gas at STP and I can't do reaction under pressure.

I lack access to scifinder.

Hexavalent - 26-11-2012 at 08:30

Where did you obtain your t-BuOH, Unintentional Chaos?

DJF90 - 26-11-2012 at 15:23

I'm off to the library in the morning so if I remember l'll do a lit search. I've looked at the preparation of BHT before using this route, but at the time I wasn't so fond of having to prepare the p-cresol (pTsOH in molten hydroxide bath). Maybe I will give it a go at some point though. I'll report back around lunchtime GMT.

Lambda-Eyde - 26-11-2012 at 16:46

I suck at doing SciFinder searches. At least I could find these ones. Maybe they will lead you somewhere. :P

I remember researching the exact same subject a while ago and found some great papers, but these were lost along with my computer (RIP).

Attachment: Alkylation of p-Cresol with tert-Butanol Catalyzed by Novel Multiple-SO3H Functioned Ionic Liquid - Chin. J. Chem. Eng. (256kB)
This file has been downloaded 1328 times

Attachment: Alkylation of p-cresol with tert-butyl alcohol using benign Bronsted acidic ionic liquid catalyst - J. Mol. Cat. A 321 ( (812kB)
This file has been downloaded 1929 times

Attachment: ALKYLATION OF PHENOL WITH t-BUTYL ALCOHOL IN THE PRESENCE OF PERCHLORIC ACID.pdf (177kB)
This file has been downloaded 653 times

DJF90 - 27-11-2012 at 03:54

So a reaxys search yielded very little. The dialkylation of p-cresol does not look to go very well or selectively. BHT of commerce is likely a mixture of mono and di-t-butyl, and of isomers also. Unless the reaction using isobutylene goes significantly better (I didn't really bother checking...). Lambda provided the better of the few papers on the subject.

Nicodem - 27-11-2012 at 08:46

Here are two articles from IEC where some industrial processes for the production of BHT are described. The reaction of p-cresol with isobutylene in a mixture of acetic acid and sulfuric acid apparently works well. I expect these conditions to be applicable for t-butyl alcohol also, though the alkylation might be slower when compared to isobutylene application. Other methods appear less suitable for such a change in the t-butylating reagent. The reaction is exothermic and thus t-BuOH should be added slowly under temperature monitoring. You might be able to use MTBE as the t-butylating reagent as well.

Also, keep in mind that the t-butylation is reversible and that the equilibrium when t-BuOH is used will not be as far to right as with isobutylene. Thus you will obtain a mixture of mono and di-t-butylated products. After distillation you can subject the monoalkylated fraction to another t-butylation, if you want a process that gives you good yields (if you care about the yields at all). Another way to achieve good yields would be to use a minimum amount of sulfuric acid catalysis (few mol%), but in such a case it is likely you would have to heat the reaction to keep it going at all. Things can get complicated if you want to optimize the reaction for selctivity/yields - the effects of the conditions is not easy to understand. Just check the related SN1 alkylation that kmno4 reported time ago.

Isobutylene is plentiful in the industry, which explains the lack of reasonable procedures using the industrially (and amateur) friendly sulfuric acid catalysis when the reaction is done with t-BuOH. Most of the examples of BHT from t-BuOH in the literature are of the academic publish-rubbish type of articles.

Alkylated Cresols from Refinery Gases
Whitney Weinrich
Ind. Eng. Chem., 1943, 35, 264–272. DOI: 10.1021/ie50399a003

Separation of Individual Cresols and Xylenols from Their Mixtures
Donald R. Stevens
Ind. Eng. Chem., 1943, 35, 655–660. DOI: 10.1021/ie50402a007

Attachment: IEC_alkylated cresols.pdf (1.8MB)
This file has been downloaded 460 times

Attachment: IEC_t-butylation of cresols.pdf (999kB)
This file has been downloaded 805 times

[Edited on 27/11/2012 by Nicodem]