2-Br-propionic acid prep Q

[ChemicalSolution]

In this procedure, is there any reason why D-alanine is used?  Given the different fractions of product collected upon distillation, SWIM assumes the stereochemistry is not preserved(?).

If D-alanine MUST be used, this sort of puts a damper on the OTC factor.

xoxo-Julia

(R)-2-Bromopropionic acid: 50 g D-Alanine (.56 mol) was dissolved in a mixture of 580 ml of 48% aqueous HBr and 1 L of water, and cracked ice added to give a total volume of 3 L. 104.3 g NaNO2 (1.51 mol ) was added in small portions with stirring, followed by 700 g of Na2SO4. When the stirred reaction had warmed to 15 degrees C, it was decanted from solids and extracted with five 500 ml portions of Et2O. Drying of Na2SO4 and then CaCl2 and concentration in vacuo gave 65 g of oil as residue. this was distilled at 25 torr collecting the forerun between 40-70 degrees C, and three fractions distilling at 104-8 degrees C (25 torr) totalling 51.3 grams.

[halfapint]

Give it up. I posted a question on bromopropionic acid, and got no response. I think there must bee a moratorium on bromopropionic answers. Everybody but us is smugly smirking in their knowledge, to watch us wretchedly wallow in our ignorance.

The chirality issue is just a red herring. It may have mattered to the original authors, that they got R-bromopropionic acid from d-alanine, but it isn't among our concerns. Dextrorotary amino acids have amazing prices. Just ignore the little d-. Racemic (dl-) would work, but the l-racemate is more likely to bee found in casual shopping.
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[ChemicalSolution]

SWIM would love to dream the etNO2 synthesis in DMSO as reported by Rhodium...  I guess she's just going to have to go down to her healthfood store and grab some l-alanine to give it a shot...

xoxo
Julia

[halfapint]

Darn, me too. I trained some bacilli and set them slaving to make me lactic acid. Got a couple or three good batches, hundreds of grams of calcium lactate, then messed it all up with dumb elementary chemistry errors, like trying to distill it out of sulfuric acid that was too concentrated. Now, well, people have got a little sensitive about my culturing bacilli in plastic buckets in the oven set on warm.    hee-hee
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[foxy2]

lactic acid is totally otc
quit messing with newbee's heads halfapint

http://www.aclu.org/congress/issues107.html

[ChemicalSolution]

Nevermind.. It does not matter what stereo isomer is used.


What is the purpose of the Na2SO4 added in the end?  To neutralize the acid by forming NaHSO4 + NaBr?



xoxo
Julia

[Rhodium]

Probably to make the water more polar by increasing the ionic strength, thereby pushing the organics into a separate layer.

[ChemicalSolution]

Then would MgSO4 work as well?

[Rhodium]

Yes, but try anhydrous sodium sulfate (H2SO4 + NaOH, followed by evap and drying) first before making changes to the synth.

[ChemicalSolution]

YES!  This should eliminate the left over HBr, no?  Na2SO4 is enough base to make NaBr from left over HBr but not ionize the carboxilic acid (like bicarb would..)

xoxo
Julia

[ChemicalSolution]

What about the mp of 2-bromo-propinoic acid (25c)?  Can this clog up a condenser?

[Rhodium]

Yes, use >30°C water in the condenser to be sure.

[halfapint]

For cultivation of bacillus delbruchii (or whatever its more contemporary binomial may currently bee) in the oven in a plastic bucket, one must cycle the oven on the lowest setting several times a day for optimum yield. Hoping all the time, that no hurried bakers come in to cook for you, who like to preheat the oven. Remember that.

Post 217079

(halfapint: "Re: Easy nitroethane in quantitative yield", Methods Discourse) relates to calcium lactate production. How to proceed to alpha-bromopropionic acid from there, is still a mystery to me. I think it's done with HBr.
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[Rhodium]

Correct, either HBr, PBr3, Br2/P or KBr/H2SO4 should work.