1 / 6

MAKING ALKYNES

MAKING ALKYNES. “DOUBLE ELIMINATION”. COMPOUNDS WITH TWO HALOGENS. If you have a compound with two halogens it can react twice (two E2 eliminations). If both halogens are on the same carbon, an alkyne is produced. The second elimination is more difficult than the

fola
Download Presentation

MAKING ALKYNES

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. MAKING ALKYNES “DOUBLE ELIMINATION”

  2. COMPOUNDS WITH TWO HALOGENS If you have a compound with two halogens it can react twice (two E2 eliminations). If both halogens are on the same carbon, an alkyne is produced. The second elimination is more difficult than the first one - it requires a stronger base. more difficult, requires a stronger base like NH2- most E2 bases will work

  3. AMIDE VS. ETHOXIDE .. .. : : N O CH2CH3 H .. H more basic (N is less electro- negative then O) less basic (O accommodates the charge better) The usual reagent is sodium amide in liquid ammonia (-33o C): The usual reagent is sodium ethoxide in ethanol : NaNH2 / NH3 (liq) NaOEt / EtOH Both are made by adding sodium metal to the solvent.

  4. EXAMPLES KOH EtOH D NaNH2 NH3 (liq) NaNH2 NH3 (liq) trans (the reaction is more difficult for cis )

  5. THE REACTION CAN BE DONE IN TWO STEPS stops here with sodium ethoxide NaOEt EtOH D NaNH2 predominantly the trans isomer NH3 (liq) (lower energy product) stronger base brings about the second step

  6. COMPOUNDS WITH TWO HALOGENS If you have a compound with two halogens it can react twice (two E2 eliminations). If the halogens are on different carbons, a diene is usually produced. KOH EtOH D NaOEt Br2 EtOH D CCl4

More Related