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Specialty Chemistry Forums => Citizen Chemist => Topic started by: zilalti on November 13, 2006, 05:29:45 PM

Title: Glycerol through acid hydrolysis of fats.
Post by: zilalti on November 13, 2006, 05:29:45 PM: Recently I've been looking for a small amount of glycerine for a few experiments and I was wondering if it could be obtained through the hydrolysis of household fats and oils. I no longer have any sodium hydroxide but I do have 98% Sulphuric acid so wondering if It could be obtained by acid hydrolysis. If possible, what kind of conditions would be needed?
Title: Re: Glycerol through acid hydrolysis of fats.
Post by: Alberto_Kravina on November 14, 2006, 12:50:09 PM: If you need some Glycerol for some experiments, just buy it....however it would be interesting to hydrolyse a fat with H₂SO₄. If you want to try it I think that the best idea would be to mix the fat with water and then add SLOWLY the sulfuric acid. No idea if this works (at home)
Title: Re: Glycerol through acid hydrolysis of fats.
Post by: zilalti on November 14, 2006, 06:15:49 PM: Thanks for the info, i'll try tonight. Also I have bought some glycerol but I just wanted the satisfaction of making it myself. The glycerol I bought was.. http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&ih=007&sspagename=STRK%3AMEWN%3AIT&viewitem=&item=170044594739&rd=1&rd=1
however reading the description again i'm not sure whether what I bought is suitable for what i'm planning to do?.
Title: Re: Glycerol through acid hydrolysis of fats.
Post by: constant thinker on November 14, 2006, 09:03:56 PM: Remember add acid to water and not the other way around. Also remember Alberto_Kravina's advice on adding it slowly.
Title: Re: Glycerol through acid hydrolysis of fats.
Post by: zilalti on November 15, 2006, 11:59:30 AM: i've made that mistake before, luckly i was wearing goggles and lab coat.
Title: Re: Glycerol through acid hydrolysis of fats.
Post by: zilalti on November 15, 2006, 05:28:05 PM: I attempted the above a few minutes ago however i'm having a few problems.

To about 10ml of cooking oil and water I added drop wise about 3ml of 98% sulphuric acid. After stirring the oil went couldy white so I took a few drops and added it to a small pile of KMnO4 hoping it would ignite but nothing happened. I then added a little more acid and heated the solutions for a few minutes and tested with KMnO4 again however this time it went dark green, which i'm assuming is Mn2O7 formed by the excess acid. Anyone know whats happening?
Title: Re: Glycerol through acid hydrolysis of fats.
Post by: Borek on November 15, 2006, 05:57:28 PM: Quote from: zilalti on November 15, 2006, 05:28:05 PM
dark green, which i'm assuming is Mn2O7 formed by the excess acid. Anyone know whats happening?

It is not Mn₂O₇. Dark green sounds more like MnO₄^2-.
Title: Re: Glycerol through acid hydrolysis of fats.
Post by: zilalti on November 15, 2006, 06:54:21 PM: I always understood that sulphuric acid and potassium permangante gave manganese heptoxide which is green?
Title: Re: Glycerol through acid hydrolysis of fats.
Post by: Borek on November 15, 2006, 07:17:56 PM: Only when dry. Besides, your solution contains enough organic substances to explode on contact with Mn₂O₇.

http://81.207.88.128/science/chem/exps/mn2o7_hs/index.html
Title: Re: Glycerol through acid hydrolysis of fats.
Post by: zilalti on November 16, 2006, 03:13:35 PM: Ah ok, thanks.