Hi. I'm on my thesis. I google how to synthesize monoacetyl hydroquinone (or hydroquinone monoacetate) , and I 've try the following:
Add: 220g hydroquinone and 500ml acetic acid into a 2 neck round flask. Then add drop by drop acetic anhyride to the mixture in one hour. then keep
the reaction mixture at 110 deg C for 2 hours. After the reaction complete, 1 liter of toluen is pour into the flask. Hydroquinone is separated and
reuse without purification. The toluen solution is distilled under vacuum, and we have monoacetylhydroquinone.
In fact, what I get is not hydroquinone alone. There are always hydroquinone and diacetyl hydroquinone in the oil after rota-vaporation.
My question are:
1/ Is there any way to purify monoacetyl hydroquinone ( i mean separate it from the mixture) without using column chromatography?
2/ Is there any simple way to prepare monoacetyl Hydroquinone?
THanks in advanced. I've stuck with this problem for weeks.Nicodem - 29-3-2010 at 11:25
In fact, what I get is not hydroquinone alone. There are always hydroquinone and diacetyl hydroquinone in the oil after rota-vaporation.
This only means that the distillation column you used is not good enough for this aplication. Get a better one and try again.
Quote:
1/ Is there any way to purify monoacetyl hydroquinone ( i mean separate it from the mixture) without using column chromatography?
The simplest is the one used in the procedure you cited (and failed to provide the reference!): vacuum distillation.
Quote:
2/ Is there any simple way to prepare monoacetyl Hydroquinone?
You mean simpler than the one you describe? No.dstrtr - 29-3-2010 at 15:55
Thanks for your reply.
Well, not vacuum distillation, but rota-vaporation under low-pressure to eliminate AcOH and Toluen.
The final oil that I get contains mostly monoacetyl hydroquinone, with a trace of diacetyl hydroquinone and hydroquinone. Is there any way that I can
rystallize this oil?
Thanks. Sorry for my English.chemrox - 29-3-2010 at 21:20
as Nicodem stated, distillation would have been indicated. Also consider using acetyl chloride instead of acetic anhydride. Use it in pyridine and
make sure the molar ratio is 1:1 hydroquinone to acetyl Cl or no more than a slight excess of the acylating agent. This is a thesis? Make a table of
all reactants and products with their physical properties and amounts in terms of mass and equivalents. This is standard for a good notebook anyway.
Drawings of the reaction, especially the electron movements, is the next thing and then the apparatus should be sketched. I wouldn't expect a clean
product from a single reaction and solvent removal except in a few rare cases.
A separation scheme should be outlined too. This would have been based on physical properties and would have indicated the proper procedures. Eg. I
recently made some phenethylpropionate (lovely smell). An extraction with base and brine removed the unreacted acids. Next the organic layer was
dried over Na2SO4 and finally a distillation with a short path still removed the small amount of alcohol left over.
[Edited on 30-3-2010 by chemrox]not_important - 29-3-2010 at 21:54
Also of possible interest :
CA1225655
EP0167464
JP61018745
FR2566392
DK281385
BR8502941
United States Patent 5183928
Preparation of hydroquinone monocarboxylates
which uses a mixture of hydroquinone and an excess of the diacetate along with a catalyst to obtain a mix of the mono and diacetates with little
hydroquinone. This suggests that aiming for a similar ratio of mono:di acetate may be the way to go. A preliminary separation could be done by
recrystallisation from water, in which the diacetate is less soluble. dstrtr - 30-3-2010 at 07:51
Thanks "not-important" for the link
Thanks chemrox a great deal for sharing the experience.
Actually I'm synthesizing alpha-arbutin, and it is necessary to synthesize monoacetyl hydroquinone as a glycosylation agent.dstrtr - 5-4-2010 at 04:07
Although hydroquinone is considered insoluble in toluene, a very small amount of hydroquinone still presents in toluene. Besides, diacetyl
hydroquinone also present. It's hard to separate the mixture of hydroquinone, monoacetyl and diacetyl hydroquinone.
Do you have some way to separate monoacetyl hydroquinone from the mixture?
Thanks.
