Hi!
Henry reaction? Under which circumstances the nitroalcohol dehydrates to form nitroalkene?
From OrganicSyntheses.org NITROSTYRENE =>Nitrostyrene can be prepared by the condensation of benzaldehyde and nitromethane. This may be accomplished by the use of small amounts of a primary aliphatic amine,1 a method which requires a number of days for the reaction to go to completion, or preferably by the use of alkali as first discovered by Thiele.2 Alternatively, nitrostyrene can be prepared from benzil, nitromethane, and sodium ethoxide,3 or from styrene and nitrosyl chloride.4
Isn't there a contradiction between the above and the below writing?
From => Organic-chemistry.org
If acidic protons are available (i.e. when R = H), the products tend to eliminate water to give nitroalkenes. Therefore, only small amounts of base should be used if the isolation of the ß-hydroxy nitro-compounds is desired.
Because one (the one theat's above) governs the use of small amounts of base if the isolation of NiroStyrenes is desired but the below writing governs that small amounts of base should be used if the isolation of the ß-hydroxy nitro-compounds is desired.
As far as I can understand to get the NitroAlcohols if the reaction is done with strong bases like NaOH he is done under low temperatures. But if he is done with weaker bases such as Amines he is done under high temperatures to get the NitroAlkenes. This might be due to the formation of Na salts of the NitroAlcohols (in the middle stage) (which is possibly the white preticipate that forms duiring the addition) which are converted into Nitrostyrenes upon the addition of the acid. -OH from the Na goes with the acidic proton of the Nitroalkane thereby creating a double bond betwen the alpha-carbon of the Nitro Compound and the alcoholic -OH group is coverted into H2O while Na is converted into NaCl creating Nitrostyrene!
But the point that I can't understand is that how is the NitroAlcohol synthesis made by the usage of NaOH? (I have got many examples for these type of reactions) Patent: EP0960876
Basically I want you to compare the above patent (Nitroalcohol Synthesis) and the preperations given below (For NitroAlkene Synthesis) and answer my question:
Organic Syntheses, Coll. Vol. 1, p.413 (1941); Vol. 9, p.66 (1929). (
http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=CV1P0413)
JOC 15, 8 (1950)
SO THE MAIN QUESTION IS THIS: Under which circumstances the nitroalcohol dehydrates to form nitroalkene? (Without the usage of dehydrating catalysts)
Thanks!