Alkynes: Methods of Preparation

University:
Brigham Young University
Course:
CHEM 553 | Advanced Organic Chemistry
Academic year:

2023
Views:

444

Pages:

13
Author:

CometCrafter

Alkynes Methods of preparation Acetylosse à a key chemical for the production of several organic com pounds of great Industrial bomportance. It is used to the manufacture of Synthetic fibers, plastic, rubber, acetaldehyde, acetic acid 4 Ethyl alcohet. As such many special methods arre used for its preparation. Some Commonly used methods are destribed belo 1. Action of water con Calcium Carbide :- Cacz +2H20 → HECH + Ca (OH)2 Calcium Combide Acetylone Catcium Carbide required for this purpose in itselt obtained by heating Coke Calcium oxible in an electric furmance CaO+30-22735 Cac + CO The above method in Suitable for Labrotong as well as Loroge Scale preparation of acetylene. The gas formed is Collected by townward displace mont of water. Haj by dehytoo halogenation of virical geom Lihalides: gt Involves double demy-tro halogenation when treated with alc. KOH et 200% of Nant₂ at 150°C. OX ①Br-CH2-CHoy-Bor. ale- KOH →CH=CH-Por -KBr. -H2D 1.2. Dibromoethane ↓ (Promoethane) MaNH2 150 HCECH +labor HBC-CH-B ale.kotl →H2C=CH-Dor 11- Dibromo-H20 thane NaMHz 150°C HC=ECH + NH3 +KBr (in) HaC-CH-CH-Dor 1 CH3 ale. Kol - H₂C-CH=CHBr ↓ Na NH₂ 150°C -KB =420 CH3C=CH + KB propyre +420 Meehamirm The darydohalogenation or Eliminatim reaction initiated by a base as shnon below. H alc. Hac c-Bor -H20 H2=CH-Br اد 041 41 C=C H HCECH NaNH2 Ettyne - NaBr - H3 (b) Pay dehelogenation of Tetrahalides! - The dehalogeration & Caused by heating the tetra halogen Compound with Zine. Heat R-C≡CH +22 B Bon CH-CH Bry+2n A →HC≡CH + 2201 B2 1.1.2.2. Tetrabrom Ethane athyne 3. Higher alkynes: Boy allkyl halide on the action of Sodium acetylide (a) Reaction of Sodium acetylide on alkyl halide gives bisher alkyne. (3) HCECH FNaNi₂- Acetylene lig. Nh HC=CNa + NH3 Sod acetylide HC=C.Na + CH₃or NaBr + HC≡C-CH3 propyne HC = cla+ Cats1 NaI + HC=C-CH2-CH3 (But-1-yne) If excess of Sodamide i used in the first mencetion, both the bystrogen atoons Substituted by ore Se di sediam acetyllde. Sellam to form (ii) HC≡CH + Na lig. NH3 → NaC=CNG +H2 disodium acctslide Nac=cNa + 2CH3 Por → 2NaBr + CA13-C= CH But-2-Yne (1) Actirs with acid on alkynides AgC=C.Ag +2HCl Di silver acetylide → HC = CH + 2 Agel Acetylene CH3-C=C.Ag +Hel→ H₂C-C≡CH + Agi propyne (c) Reactim of acetylene Magnesium halide with alkylhalide gives hisher albeynes. HC = CH + CH3 mg I → HC = C. Mg I + CHy Cacemlone mag Lodide) HC = C. Mg2+ CH31 → HC=C-CH₃+MgI propyne Mechamam R = 24 + CH₃Mgxc RC= Emyx R=2H+ C -Mg x2 RC=ER Disher alkyne