SATURATED HYDROCARBON

8/7/2019 SATURATED HYDROCARBON

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SATURATED HYDROCARBON

Synthesis of alkanes

Hydrogenation of alkenes

An example of addition reaction

Hydrolysis of Grignard reagent

(alkylmagnesium halide)

Wurtz reaction (Reduction of alkyl halide)



Reaction of Alkanes

Combustion

Halogenation

A reaction where a halogen replaces one or more hydrogen

UNSATURATED HYDROCARBON

Synthesis of alkenes

dehydrogenation of alkanes:

X = Y = H

dehydration of alcohols:

X = H; Y = OH

dehydrohalogenation of alkyl halides:

X = H; Y = Br, Cl

Synthesis of alkenes: elimination reactions



Dehydrogenation of alkanes

Elimination of molecule H2

limited to industrial synthesis of ethylene, propene

Dehydration of alcohol

Loss of H and OH from adjacent carbons.

Acid catalyst is necessary.



Regioselectivity in alcohol dehydration

A reaction that can proceed in more than one

direction, but in which one direction predominates,

is said to be regioselective.

Zaitsev Rule

When elimination can occur in more than one

direction, the principal alkene is the one formed

by loss of H from the carbon having the

fewest hydrogens



Dehydrohalogenation of alkyl halides

Loss of H and halogen (X) from an alkyl halide

In the presence of strong base in solvent likewise

Reactions of alkenes

Primarily reactions involve the double bond

The key reaction of double bond is addition reaction

(Breaking the bond and adding something to each carbon)

The major alkene reactions include additions of hydrogen

(H2),halogen ( CI2 or Br2), water (HOH) or hydrogen

halides (HBr or HCI)



Hydrogenation Addition of H2

Addition of a molecule of H2

Results in the formation of an alkane

Usually requires heat, pressure and a catalyst like Pt, Pd or Ni

Hydration: Addition of H2O

The addition of water to an alkene

produces an alcohol

One carbon get an H, the other an OH

The reaction requires a small amount of acid to be present

to work.

Markonikovs Rule

The carbon with the most carbon-hydrogen bonds initially,

will recieve the hydrogen.

Only valid if the alkenes is unsymmetrical



Always look for the carbon with the most hydrogen. It

will get the additional H.

Hydrohalogenation

Addition of HX to an alkene

HX HF, HCI, HBr, HI



It follows Markonikovs rule where the H ends up on the

carbon with the most hydrogen to start with

Halogenation: Addition of X2

The addition of halogen to an alkene

produces a haloalkane or alkyl halide

Synthesis of alkynes

Dehydrohalogenation of dihaloalkane



i. Geminal dihalide

Dehydrohalogenation of dihaloalkane

ii. Vicinal dihalide



Reaction of alkynes

Hydrogenation of Alkynes

Hydrohalogenation of alkynes

Follow Markonikovs rule

Alkynes are slightly less reactive than alkenes



Example

Hydration of alkynes



Example

Synthesis of Alcohols

Alcohols can be prepared by the hydration of alkenes or by the reduction of aldehydes,

ketones, acids, and esters.

Hydration of alkenes

The elements of water can be added to the double-bonded carbons of an alkene in either a

Markovnikov's or an anti-Markovnikov's manner. As shown in the following figure, a

hydrogen ion catalyzes the Markovnikov's addition.

The anti-Markovnikov's addition results from a hydroboration-oxidation reaction.

Reduction of aldehydes and ketones



An aldehyde has a structural formula of

while the structural formula of a ketone is

In these formulas, the R or R group may be either an aliphatic or aromatic group. In a

ketone, the R and R groups may represent the same group or different groups. These types

of compounds are best reduced by complex metal hydrides, such as lithium aluminum

hydride (LiAlH4) or sodium borohydride (NaBH4).

Following are two examples of complex metal reductions:

Lithium aluminum hydride is a very strong reducing agent that will reduce many functional

groups in addition to aldehydes and ketones. Sodium borohydride is a much weaker

reducing agent that basically will reduce only aldehydes and ketones toalcohols.

You can also catalytically reduce aldehydes and ketones to produce 1° and 2° alcohols.

Reduction conditions are very similar to those used to reduce alkene double bonds. If amolecule possesses both a double bond and an aldehyde or ketone functional group,

reduction of the aldehyde or ketone group is best carried out using sodium borohydride. The

reduction of cyclohexanone by hydrogen gas with a platinum catalyst produces cyclohexanol

in good yield.

Reduction of carboxylic acids

The reduction of a carboxylic acid:



leads to the formation of a primary alcohol:

This reduction requires a very strong reducing agent, and lithium aluminum hydride is the

standard choice.

Diborane, B2H6, also reduces carboxylic acids to alcohols.

Catalytic hydrogenation gives very poor yields and is not usually used for this type of

reaction.

Reduction of esters

Esters, like carboxylic acids, are normally reduced with lithium aluminum hydride. In these

reactions, two alcohols are formed. An example is the reduction of methyl benzoate to

benzyl alcohol and methanol.



Grignard reaction with aldehydes and ketones

The Grignard reaction is the only simple method available that is capable of producing

primary, secondary, and tertiary alcohols. To produce a primary alcohol, the Grignard

reagent is reacted with formaldehyde.

Reacting a Grignard reagent with any other aldehyde will lead to a secondary alcohol.

Finally, reacting a Grignard reagent with a ketone will generate a tertiary alcohol.

Synthesis of Aldehydes and ketones

Oxidation of 10 Alcohol

General equation :



Oxidation of primary alcohols to aldehyde using pyridium chlorochromate (PCC) in

anhydrous media such as dichloromethane.

ii) Hydration of Alkynes

General equation :

Keto- Enol Tautomerism

The name enol is derived from the IUPAC designation of it as both an alkene (-en-) and

alcohol (-ol).



Keto and enol forms are examples of tautomers, constitutional isomers in equilibrium

with each other that differ in the location of hydrogen atom and a double relative to a

heteroatom, most often O, S, or N.

This type of isomerism is called tautomerism.

O OH

|| |

CH3-C-CH3 CH3 -C = CH2

acetone acetone

(keto form) (enol form)

Ozonolysis of Alkenes

General equation :

Hydrolysis of Gem Halides

To produce aromatic aldehyde



Reaction and Synthesis of Carboxylic Acid

The classic synthesis is the Fischer esterification, which involves treating a carboxylic acid

with an alcohol in the presence of a dehydrating agent:

RCO2H + R'OH RCO2R' + H2O

Ester hydrolysis

Acid-catalyzed reaction

Reaction of esters

Soap formation (Saponification)



Reaction Of Amines

Tertiary Amines have no hydrogen atom and three alkyl or aryl groups attached to the

nitrogen

ALIPHATIC: trimethylamine, ,

ethyldimethylamine, ,

diethylmethylamine, ,



Reaction Of Amides

The CLASSIFICATION system for alcohols, amines and amides

Functionalgroup of the

homologous

series

PRIMARY SECONDARY TERTIARY Comments

ALCOHOLS

Phenols are

NOT

classified in

this way. The

ease of

oxidation

and nature

of product isaffected by

the class of

the alcohol

examples of

alcohols butan-1-ol

propan-2-ol 2-methyl-

propan-2-ol

examples of

alcohols

AMINES

There are

prim/sec/ter

t aliphatic

(alkyl) or

aromatic

(aryl)

amines. See

also Note 3.



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SATURATED HYDROCARBON

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