Question

typo: chemdoodle just means computer drawn

chemdoodle = computer drawn

The following pre-lab tasks must be performed individually, typed and printed out and brought to the lab for the first experimental session. Do not use your lab notebooks for this purpose. 1. Using ChemDoodle software draw a reaction mechanism (appropriate arrows, transition states, lone pairs) of imine formation upon reaction of aniline with benzaldehyde. 2. Imines are important synthetic intermediates. Provide synthetic scheme -not mechanism (ChemDoodle drawn) showing synthetic transformation using imines (synthesize new compounds using imines as starting material). Please refer to organic chemistry textbook or provided article. Cite literature. 3. How does water interfere with imine synthesis reaction? Please explain in short paragraph (15 sentences max.) 4. What are the ways of removing water as a by- product during various reactions in organic chemistry? Please list at least 3 of them. 5. What are molecular sieves? Please explain in short paragraph the chemical composition/ structure (10 sentences max.) of it. The following pre-lab tasks must be performed individually, typed and printed out and brought to the lab for the first experimental session. Do not use your lab notebooks for this purpose. 1. Using ChemDoodle software draw a reaction mechanism (appropriate arrows, transition states, lone pairs) of imine formation upon reaction of aniline with benzaldehyde. 2. Imines are important synthetic intermediates. Provide synthetic scheme - not mechanism (ChemDoodle drawn) showing synthetic transformation using imines (synthesize new compounds using imines as starting material) Please refer to organic chemistry textbook or provided article. Cite literature. 3. How does water interfere with imine synthesis reaction? Please explain in short paragraph (15 sentences max.) 4. What are the ways of removing water as a by- product during various reactions in organic chemistry? Please list at least 3 of them. 5. What are molecular sieves? Please explain in short paragraph the chemical composition/ structure (10 sentences max.) of it.

Answer 1

1) Formation of imine: Imine contains -C=NH or -C=NR group. This can be formed by treating primary amines with aldehyde or ketones in the presence of an acid catalyst. Acid catalyst helps to eliminate water molecule. In case of base catalyst the reaction is very slow. The reaction and mechanism of formation of imine is written as follows.

Aniline (primary amine) reacts with benzaldehyde (aldehyde) to form an 'benzylidene aniline' (imine) takes place in the presence of acid catalyst.

Reaction NH - H,O aniline benzaldehyde N,1-diphenylmethanimine

Mechanism H+ NH OH N. 1-diphenylmethanimine

2) Reaction of imine as intermediate or starting material:

a) Aromatic imines reacts with electron rich alkene to form an cyclic condensed product. This reaction is also known as Povarov reaction. It takes place in the presence of Lewis acid such as boron trifluoride.

BF + H3C BF CH2 CH3 он N,1-diphenylmethanimine ethoxyethene 2-phenylquinoline

b) Iminium ion or salt reacts with reducing agent NaBH3CN to get an reduced new product N-benzylaniline

Ht NaBH,CN H N,1-diphenylmethanimine Iminium ion N-benzylaniline

3) During the synthesis of imine, the byproduct formed is water. If the more byproduct formed during the reaction, then there is a chance of attack of -OH group present in the water molecule on the double bond of imine. This disturbs the reaction equilibrium. Here -OH group of water acts as a nucleophile and reversible reaction occurs and again we will end up with same aldehyde and amine. So, while synthesizing imine, its important to remove the byproduct water.  

NH H,o 1 Ht N.1-diphenylmethanimine aniline benzaldehyde

4)

1. The mixture of product can be shake with molecular sieve 4A along with chloroform (CH2Cl2) and it will absorb the water molecule.
2. Lyophilization method can be used to remove water content from bulk compound.
3. Can add magnesium sulphate in the reaction mixture to get rid of water

5) Molecular sieve is a material which contains pores of uniform size. The pore diameter is small as the small molecules, so, larger molecule will not absorb here but small molecules can easily absorbed. So, we can separate mixture of two substances.

These are the crystalline solid substance which is especially a zeolite which can permit to pass small size molecules.