Reactions of Alkynes

Reaction of Alkynes Basic Chemistry_D Chemistry_Derio erio Gusvand Gusvandi_RSA1C111014 i_RSA1C111014

With the fog of electrons (bonding π) surrounding the σ bond, alkyne compound is a nucleophile, which will react with an electrophile. Alkyne has two π bonds, so it can mengadisi to 2 molecules, depending on the reagents and conditions.

Alkyne compound is less reactive than alkene compounds.

The relative stability of several carbocations:

1.

Addition of Hydrogen Halides

Addition of hydrogen halides (HX) on the last alkyne compounds similar to those seen in the alkene compounds. If the triple bond is at the end of the alkyne compound (terminal alkyne), the H + will be bound to the sp carbon atoms that have bonded with hydrogen, hydrogen, producing secondary secondary vinyl cation (according to the Markovnikov rule).

REACTION MECHANISM

Suppose for the reaction between HCl with alkyne compound: • π bond is relatively weak will split because the electrons in the  protons  protons on the the electrophile electrophile compound compounds. s.

π

bond was withdrawn by the

• Intermediate in the form of positively charged carbocation will quickly react with the negatively charged chloride ions.

• If the addition of HX occurs in an internal alkyne, it will form two kinds of geminal dihalides, the first proton adducts can occur at C-2 or C-3 (carbon sp) with the same ease.

2.

Water Addition

With the acid, alkyne compounds undergo addition reactions in water.

In the case of water addition reactions, terminal alkyne is less reactive than the internal alkyne. Terminal alkyne would mengadisi water if Hg2 + ion is added to the reaction mixture acidic.

3.

Hydrogen Ad Addit dition A.

Catalytic hydrogenation of alkanes With the presence of metal catalysts such as Pt, Pd or Ni, alkyne compound may be a compound of hydrogen alkanes additioned.

Catalytic Catalytic hydrogenatio hydrogenation n takes 2 stages with intermediate form alkene compounds. compounds. With an efficient catalyst such as Pt, Pd, or Ni, the reaction may be terminated only on the product product alkene.

B.

CIS-catalytic hydrogenation of alkenes Alkyne hydrogenation of alkenes can be stopped at this stage by using a catalyst partially deactivated. Lindlar catalyst is a catalyst made of Pd and poisoned with quinoline. Nickel  boride (Ni2B is the latest latest alternative alternative to Lindlar Lindlar catalyst catalyst that made made it easier easier and gives  better results. results.

4.

Halogen Adducts

Bromine and chlorine could mengadisi the alkyne as occurs in alkenes. Jika1 mol mol alkyne  pada1 mengadisi mengadisi halogen, halogen, it will will produce produce dihaloalke dihaloalkena. na.

5.

Halogen Halide Adducts

Hydrogen halide (HX) can mengadisi the three compounds alkyne bond as occurs in addition to the two compounds alkene double bond, with the initial product is the vinyl halide. If HX adduct the alkyne end, it will produce products with Markovnikov orientation following the rules. Second adduct of HX molecule orientation as the first.

MECHANISM

If 2 mol mol HX adduct to 1 alkyne, then the second mole adduct usually the same orientation with the first addition.