[bhkuk]

i want to make an addition of (R)-(+) methyl p-tolyl sulfoxide to 2,3-o isoprpylidene D-glyceraldehyde
i will give detalis about the procedure:
a solution of the sulfoxide in THF was slowly added to solution of LDA in THF at -78C and the mixture was stirred for1 hour.
then asolution of aldehyde was slowly added at the same temperature, the reaction was stirred for 1 houre and allowed later to reach room temperature.
then the reaction quenched with saturated ammonium chloride,and extracted with dichloromethane
the organic layer dried and the solvent was removed under reduce pressure and the residue purified by flash chromotografhy.
1. why should i use THF as solvent? is it creat any stability to the LDA?
2. why should i stirr for such long time? is it because the low temperature? why do i need the temperature of   -78C?
3.what is the role of the ammonium chloride?
4. do you know good internet site that can give me good learning of flash chromotography and other ways of methods of chromotography?

[Dan]

1. why should i use THF as solvent? is it creat any stability to the LDA?
2. why should i stirr for such long time? is it because the low temperature? why do i need the temperature of   -78C?
3.what is the role of the ammonium chloride?
4. do you know good internet site that can give me good learning of flash chromotography and other ways of methods of chromotography?

1. You require a solvent that:

a) Won't freeze at -78C
b) Will dissolve your reagents
c) Is chemically inert to your reagents. You are useing a very strong base, so you require an aprotic solvent

THF just fits the bill

2. I wouldn't call 1 h a long time. -78C is used because your reagents are extremely reactive and so may cause unwanted side reactions/decomposition at higher temeratures.

3. Quenching your reaction essentially means destroying/neutralising excess reagent. Ammonium chloride is a weak acid... think about what you are generating in your reaction, why do you need a proton source at the end?

4. See any practical organic chemisrty textbook, and some general organic texts cover it (eg. Clayden, Greeves, Warren & Wothers).