unsaturation in fatty acids

[dilipsingh]

hi i need a help in organic chemistry regarding a problem,which i googled but unable to find to find solution my problem is"i want to convert saturated fatty acids into unsaturated fatty acid and i was thinking to use alchoalic KOH but it will rahter give saponifiaction reaction, i want to know a simple and easy reaction or any regent which i can use to create unstauration (double bond in any number) in fatty acid which i can carry out in my biotechnology lab,,,since my background is biotechnology not chemistry, so i need a serious suggestion from the member of this group

thank you

[John Cuthber]

I don't think there is a simple way to do it.

You can halogenate the fat then hydrolyse that halide to give an alcohol then dehydrate that to give an unsaturated product but, at best, it won't work very well.

[Suxamethonium]

Do you have to start with a saturated fat? There are a few ways to synthesis (poly)-olefins, off the top of my head the Suzuki reaction comes to mind. But I can't really see a reaction that will give a good yeild of the particular unsaturated fats that you want from the saturated compound. Seeing as the carboxylate head is the most reactive part of the chain- it's very possible to replace it with an extended carbon chain that contains a double bond then put a carboxylate on the 'new end'.

 

There are numerous way to go about this, but for example the following :

 

R- COOH -> R-COOMe -> R-C(=O)-CH₂-CH=CH-CN -> R-CH(=O)-CH₂-CH=CH-COOH

 

At step three you can decide to remove the ketone to leave either CH₂ or reduce before hand to create an OH to dehydrate a final compound with R-CH=CH-CH=CH-COOH. (I just left the ketone alone in the above schematic).

 

Of course, the effect of this method would be that the new fatty acid would also be longer than the original saturated acid- which may not suit the parameters you require.

[hypervalent_iodine]

Do you have to start with a saturated fat? There are a few ways to synthesis (poly)-olefins, off the top of my head the Suzuki reaction comes to mind. But I can't really see a reaction that will give a good yeild of the particular unsaturated fats that you want from the saturated compound. Seeing as the carboxylate head is the most reactive part of the chain- it's very possible to replace it with an extended carbon chain that contains a double bond then put a carboxylate on the 'new end'.

 

Suzuki reaction can work for those sorts of systems, but as you say the yields will likely be low and you will get byproducts.

 

OP, is there any reason you can't purchase these compounds as you want them? The process for doing this and purifying your product is going to be arduous and expensive for you in the long run and you'll most likely have to do it a few times before you get the hang of it. If you can buy it, I would try go for that route.

[Suxamethonium]

Suzuki reaction can work for those sorts of systems, but as you say the yields will likely be low and you will get byproducts.

 

Lol- I jumped straight in and forgot to mention buying the reagents *facepalms*

 

Also in reference to the synthesis... If it is absolutely essential to start from a saturated fatty acid and progress to a non saturated one (i.e. you can't buy them for whatever reason) then I think the best bet would be to try using fatty acid desaturases? This will also provide the ability to selectively decide what carbons the double bond(s) form between and will also give cis- selectivity (which could be changed to trans synthetically... [palladium chemistry? I'm not 100% sure, but it should be easy enough to find out])...

[dilipsingh]

Hello

 

thank you all for ur suggestions

its not about buying the saturated one actually i have standardized a colorimetric assay (sulfo-vanillin phosphoric acid assay) to quantify lipids from whole algal cells without extracting them but the problem is it gives reaction with only unsaturated fatty acids not with saturated one, leading to flaw in this protocol. so what i was thinking to treat standard saturated fatty acids (SFA) to create double bond in it,so this regent will react with double bond and will give positive reaction

 

and fatty acid desaturaes i cant use at high temp along with higher conc. of H2SO4.

since i am doing my phd in biodiesel field so it is important to quantify extact amount of lipids in whole cell.

what about first halogenation followed by dehydrohalogenation (with alc KOH, elemination reaction) any idea???????/

[Suxamethonium]

Fatty acid desaturaes i cant use at high temp along with higher conc. of H2SO4.

 

Could you do the reaction before heating/acidifying?

 

To chlorinate a saturated alkyl chain will require the use of chlorine radicals. These will pull apart at everything organic in the vacinity of the radicals. No doubt you will get some attaching to the alkyl chain- but also to the rest of the compounds in the assay. Its predictability is low and I would imagine reproducibility would be low also. You would also be assuming to get near 100% yields which is fairly rare as far as organic reactions go, especially in a two step process.

 

Note, in such reactions you are likely to get mixes of cis and trans products- (however some reactions favour one or the other depending on conditions) so you would also need to work out if the assay detects trans fats.

 

I feel that your best bet would be to find some way to make the enzymatic process work- because synthetically your options are fairly limited and would probably not work reliably without at least extracting the fatty acids from the rest of the cell components first.

 

My other suggestion would be using a different essay to find out the saturated fat content?

[hypervalent_iodine]

If you were to go that way, doing it on whole algal cells would not work and you would have to purify them, which of course leads to the issue of product loss and results that are less than they should be. As well, your yields won't be 100%, as stated above, and you will likely get a very wide array of byproducts, which will again not translate well in your results; and this is ignoring the fact that some of the fatty acids you extract will already have double bonds in them (some of them will have multiple).

 

I would go with what Suxomethonium suggested and try and find other protocols for quantifying the lipids. I can't imagine it would be too difficult to find one, given all the recent interest in algae as biofuel feedstocks.

[John Cuthber]

I get the feeling that you are looking at the "low technology" end of the range of options. If I'm wrong then use HPLC /MS.

There's no way of selectively introducing double bonds into the lipids that won't also introduce them into other things- for example the side chains on some amino acids.

Also, that method would introduce different numbers of double bonds randomly into the fatty acids. That would give rise to different sensitivities for the different acids. It would be impossible to get a meaningful result that way.

You would be better filtering the algae out, drying them, weighing them, washing them with ether and drying and weighing them again. The weight loss is mainly due to lipids.

[dilipsingh]

Hello all

 

this was assay i standardized for initial quantification of lipid without extracting them. This assay is cost effective, fast and can be scaled up for large numbe rof samples for initial qunatification of lipid from whole cell. I have studied the reaction mechanism of this assay from literature and it show that vanilin-PA regent selectively reacts with one double bond per molecule of fatty acids irrespective of more than one double bond.

 

Traditionally initial quantification of lipid is, first you have to lyse the cells then isolates lipid which is time consuming,solvent consuming since extraction efficiency is not 100

% so compormising with results. So with assay i can quantify lipid of large number of samples within short span of time.

[John Cuthber]

"So with assay i can quantify lipid of large number of samples within short span of time."

But it gives the wrong answer.

If you are happy with the wrong answer why not just make up the result? That's even quicker and easier.

[Suxamethonium]

Hmmm, you could lyse the cell, use desaturase and then use vanilin-PA... Lysing the cells isn't that much extra time- and i reckon the desaturase could just be left over night. I'm pretty sure desaturase wont effect any of the other lipids (like those in the membrane) so you should get an acurate result. You could always do the isolation essay a few times to compare/validate the results and confirm this.