[magician4]

I used a reflux condenser & Pt/C+D2O+Benzne system @180C & H2 atmosfer,

this doesn't sound like a method to achieve H-D exchange in benzene, but like a method to reduce benzene to cyclohexane instaead


regards

Ingo

[Archer]

I used a reflux condenser & Pt/C+D2O+Benzne system @180C & H2 atmosfer,

this doesn't sound like a method to achieve H-D exchange in benzene, but like a method to reduce benzene to cyclohexane instaead


regards

Ingo

I misread the temperature as 80°C rather than 180°C! This is impossible to achieve in an open system when you are working with a benzene / water mix.

At the sort of pressure that you would achieve in an autoclave at that temperature (which is the only way to do this) you may well hydrogenate as Ingo has rightly pointed out.

You may wish to consider treatment of benzene with D₂SO₄ for this reaction.

[Enthalpy]

Wouldn't it be better to avoid all H in the synthesis, since it's difficult to separate from D?

Maybe with dry C₂Ca and D₂0 to get C₂D₂, then transform it to C₆H₆?

Please take with caution, I'm bad on such matters.

[Archer]

Wouldn't it be better to avoid all H in the synthesis, since it's difficult to separate from D?

Maybe with dry C₂Ca and D₂0 to get C₂D₂, then transform it to C₆H₆?

That sounds promising but maybe more suited to industrial production. I am not sure how easy this would be as a bench scale preparation as prohibitively high temperatures are required.

[magician4]

That sounds promising but maybe more suited to industrial production.

unfortunately, the opposite is true:

yes, this can be done ( Reppe did it) , but won't give you that great yields, and a raw product with like 12% styrene in it  (which is difficult to separate)

... whereas benzene / D⁺ / D₂O will work "quantitatively" (i.e. within statistical distribution of D/H) , with no loss of D and the option to work up the water thereafter

deuterium, after all, is a bit expensive

regards

Ingo

[Archer]

That sounds promising but maybe more suited to industrial production.

unfortunately, the opposite is true:

yes, this can be done ( Reppe did it) , but won't give you that great yields, and a raw product with like 12% styrene in it  (which is difficult to separate)

... whereas benzene / D⁺ / D₂O will work "quantitatively" (i.e. within statistical distribution of D/H) , with no loss of D and the option to work up the water thereafter

deuterium, after all, is a bit expensive

I stand by my original suggestion;

You can readily purchase it

Would save a lot of time and effort for this one, let someone doing batch production worry about the recovery of Deuterium and make the molecule for you.

[Enthalpy]

Making instead of buying is a small hint that the amount is significant...

Can styrene (-30°C) be separated from benzene (+5°C) through the melting temperature? In a freezer. OK, I understand the polymerization of acetylene yields many more unwanted things, and that benzene must make eutectics with many aromatic compounds, but if some benzene too is recycled, it's nothing tragic.

One thing I like with just hydrocarbons, all fully deuterated, is that deuterium can be recovered from the unwanted compounds by pyrolysis. Or by full combustion, since the C₂Ca route needs D₂O.

[magician4]

Making instead of buying is a small hint that the amount is significant...

@jalal5 was talking like 100 mL in his original posting
those you could buy NMR-grade (i.e. 99.5 % D) for 272 Euro CIF (367,20 US-$)

and remember: "making" requires D₂O anyway, which goes at 115 Euro (155,25 US-$) 100 mL , 99.8 % D


.. which makes this whole endeavour kind of pointless, in my opinion

regards

Ingo

[408]

Now it looks like it needs to be under pressure mostly because of the BP of benzene.  Why not do the exchange on benzoic acid and then decarboxylate?


Or phone aldrich... 

[Archer]

Making instead of buying is a small hint that the amount is significant...

How much time and effort have you already spent on this endeavor?

Now you are considering other methods which require specialist high temperature / pressure equipment.

Also, have you considered how you intend to store the acetlyene-d₂ once it had been prepared?

RE selective crystallisation of styrene, it is too soluble in benzene to achieve this. You could polymerise it but this is all a lot of effort for very little gain.

Your best bet is either the literature procedure I linked to you (or finding a more contemporary method in the literature) or just accepting the high cost of deuterium labelled organic compounds.

[Enthalpy]

Jalal5 made the original post - I only suggested the C₂D₂ route, but I'd support purchasing C₆D₆. Unless, of course, the amounts exceed vastly 100mL.

Oops, my apologies to Hunter2 who suggested the C₂D₂ route before I did:
http://www.chemicalforums.com/index.php?topic=70989.msg256204#msg256204

The required purity would be an important hint. Merck and Sigma-Aldrich propose it at 99% benzene purity, with 99.5% or 99.95% deuterium purity. Starting with C₆H₆ and replacing H with D means that the source of D must be >99.5% pure even after it exchanged with the H of C₆H₆, which means >>200 times the amount needed. The 200x figure improves if done in sucessive purity steps, but is a hard limit. That's why I (Hunter2 must have the same reason and maybe others) consider avoiding any H right from the beginning.

[curiouscat]

Can styrene (-30°C) be separated from benzene (+5°C) through the melting temperature?

Why go for fractional crystallization when Styrene - Benzene Boiling points are quite wide apart?

What am I missing here?

[curiouscat]

The required purity would be an important hint. Merck and Sigma-Aldrich propose it at 99% benzene purity, with 99.5% or 99.95% deuterium purity.

You are hinting the OP wants a higher purity than what Sigma is selling?

[Enthalpy]

Curiouscat: sorry, I altered my previous post while you asked about purity - bad practice from me. My answer was about the purity of the D source after exchange with C₆H₆.

Separate from styrene by boiling: unstabilized styrene seems to polymerize quite easily, but low pressure and room temperature might work., Or as Archer suggests, get rid of styrene by polymerizing it. Needs a H-free initiator, or just heat.

[curiouscat]

Separate from styrene by boiling: unstabilized styrene seems to polymerize quite easily, but low pressure and room temperature might work., Or as Archer suggests, get rid of styrene by polymerizing it. Needs a H-free initiator, or just heat.

Styrene is quite routinely fractionated on an industrial scale I think.

All you need is a decent (not spectacular) vacuum & sometimes a stabilizer at ppm levels.

In any case, here benzene is your desired product so that'll come as the distillate. If some of the Styrene polymerizes as bottoms during distillation so be it.