Home » Introduction to Multistep Synthesis Organic Chemistry.

Introduction to Multistep Synthesis Organic Chemistry.

Multistep Synthesis.

Organic chemistry is a branch of chemistry that deals with the reaction of organic molecules. During the study of organic chemistry, one is introduced to different functional groups. These functional groups include alcohol, alkene, carboxylic acids, alkane, esters, ethers, alkyl halides, ketones, aldehyde, and so on.

To know how the reaction proceeds, it is important to know how to identify the functional groups of different molecules. Knowing these functional groups will help you know what reagent is required to convert one molecule to another.

Condition for multistep synthesis reactions.

Correct reagent.

A reagent is a chemical substance used to convert one molecule to another. The reagent must be correct and in the right concentration to get the correct product.

There must be a good nucleophile. 

A nucleophile is also called a Lewis base. It is a substance that has lone pairs which can be donated. It readily gives electrons to form a new covalent bond. Examples of nucleophiles are H2O, NH3, Cl-, Br-, I- etc.

Presence of an electrophile

An electrophile is also called a Lewis acid. It is a substance that has empty orbitals and can accept electrons from a nucleophile. For an atom to be a good nucleophile, it must be bonded to an electronegative atom in that a bond is broken when a nucleophile approaches. An example of an electrophile is a carbon bonded to an alkyl halide or a carbonyl carbon.

A leaving group.

A leaving group is a substance that cleaves when a nucleophile forms a new bond with the electrophile. It might be present or not, depending on the compound. For instance, a leaving group is unnecessary if it’s a carbonyl carbon.

The reactions of alkene and alkyl halide are the most common substance that confuses many students. This is due to the number of reactions they can undergo to form different products.

Reactions of alkyl halides. 

Before writing the reaction synthesis, we must first understand what alkyl halide looks because different alkyl halides undergo different reactions.

The four classes of alkyl halides are;

  • Methyl alkyl halide
  • Primary alkyl halides are also denoted as 10 alkyl halides.
  • Secondary alkyl halides are also denoted as 20 alkyl halides.
  • Tertiary alkyl halides are also denoted as 30 alkyl halides.
classes of alkyl halides

Reactions of alkyl halide. 

Alkyl halides undergo substitution or elimination reactions because of the good leaving groups. The conditions and reagent will determine if the reaction will be an elimination or substitution reaction.

A substitution reaction is a reaction in which another substance replaces an alkyl halide. Under these reactions, compounds undergo either SN1 or SN2 reactions depending on the reagents given.

Example of SN1 reaction of alcohol to an alkyl halide.

SN1 reactions of alcohol to alkene

Example of SN2 reaction of alcohol to an alkyl halide.

SN2 reaction of alkyl halides

An elimination reaction is a reaction in which an alkyl halide is converted to an alkene. Under an elimination reaction, compounds undergo either E1 or E2, depending on the reagent.

Examples of E1 reaction of the alkyl halide to an alkene

Example of E1 reaction of alkyl halide to alkene

 Alkyl halides are good leaving groups because they are very stable after cleaving.

Examples of E2 reactions of alkyl halides to form alkene;

E2 reactions from alkyl halide to alkene

Multistep synthesis examples.

In these reactions, several steps convert one compound to the desired compound. It could be two steps or more. The following reactions are examples of multistep synthesis.

1) Multistep synthesis for the conversion of alkene to a ketone.

An example is when alkene is converted to a ketone. To achieve this, an alkene is first converted to alcohol by a suitable. Then using a suitable oxidizing agent, the alcohol is then converted to a ketone.

Conversion of alkene to ketone

2) Multistep synthesis of benzilic acid from benzaldehyde.

The reaction mechanism for converting benzaldehyde to benzylic acid is shown below.

Steps: 

  • The reaction of two benzaldehyde molecules with thiamine hydrochloride to form benzoin.
  • Benzoin is converted to benzyl using nitric acid (HNO3)
  • Lastly, benzyl is converted to benzylic acid using potassium hydroxide in alcohol in acid. (KOH in Alcohol, then H3O+).

Reactions steps are;

Multiple synthesis benzilic from benzaldehyde

3) Multistep reaction for the conversion of benzene to benzaldehyde. 

This reaction can be achieved via several routes. Some of the routes are

1st route:

  • Benzene is reacted with Br2/FeBr3 to form bromobenzene
  • Bromobenzene is reacted with Mg in ether to form a Grignard reagent which will later act as the nucleophile.
  • The reaction of the Grignard reagent with formyl chloride.
Synthesis of benzene to benzaldhyde

2nd route;

  • Benzene is reacted with CO followed by HCl, anhydrous AlCl3.
conversion of benzene to benzaldehyde

3rd route:

  • Benzene is reacted with CHCl3, followed by NaOH.
reaction of  3-benzene to benzaldehyde

4) Multistep synthesis of benzene to m-bromo aniline.

Steps

  • Benzene is converted to nitrobenzene using HNO3 & H2SO4.
  • Nitrobenzene is converted to 3-bormo nitrobenzene using Br2 and FeBr3
  • 3-bormo nitrobenzene is converted to m-bromo aniline using Fe in HCl.
synthesis of bromoaniline from benzene

These are just examples of multiple syntheses among many. If you need help with organic chemistry homework, click on the link below, and we will be glad to help.

Importance of organic multistep synthesis. 

Synthesis reactions help chemists and researchers to synthesize compounds that do not occur naturally in the lab. Pharmaceutical companies use organic multistep synthesis to produce drugs such as aspirin and penicillin. Other drugs formed by multistep synthesis are tamoxifen, quinine, rufinamide, etc. this is why organic chemistry is important in biology.

Multistep synthesis homework help

The organic chemistry course is very broad, and most students find it difficult to understand these complex syntheses. If you have organic chemistry homework that you need help with, we have organic chemistry expert tutors who are willing to help you with your chemistry assignment.

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