Plz solve this chemistry problem (& give ur opinion abt its suitability for High School Students)?

Question

On oxidation each of the 2 aromatic compounds A & B of the same molecular wt 120 gives the same dibasic acid that on heating forms an anhydride. The compound A forms crystalline orange precipitate with 2,4 dinitrophenyl hydrazine. A on treatment with CH3MgBr, followed by dehydration and hydrogenation gives B. Identify A, B and give reactions.

Answer 1

There are quite a lot of clues in this problem that can lead to the right answer, provided the teacher touched the relevant subjects before in the course..

A dibasic acid which on heating forms an anhydride and which you get from oxidizing an aromatic compound: The most likely compound to fill this criteria is phthalic acid/phthalic anhydride.

So we are looking for an aromatic compound, mass 120 AMU, with two neigboring substituents along a carbon atom.

The aromatic rest will be C6H4, a molar mass of 76. Leaves 44 AMU for the substituents. Substract 24 for two carbon atoms, you get a rest of 20AMU - sufficient for 1 oxygen atom and 4 hydrogen atoms (compound A) or 1 nitrogen atom and 6 hydrogen atoms (a candidate for molecule B) or 1 carbon atom and 8 hydrogen atoms (another candidate for B)..

Let's tackle compound A first. The substituents are made up of 2C, 1O and 4 H. This leads to the functional substitunents CHO (an aldehyde) and CH3 (a methyl group). Voila, compound A is ortho-methyl.benzaldehyde, C8H8O..

An aldehyde forms crystalline orange precipitate with 2,4 dinitrophenyl hydrazine, so this assumption is confirmed.

An aldehyde reacts with grignard-reagent (e.g. C3MgBr) forming a secondary alcohol. Such a secondary alcohol can be dehydrated into an alkene, which after hydrogenation will become an alkane. This seems to be the way we get to compound B. No nitrogen involved, so compound B will be ortho-ethyl-methyl-benzene.

Here's are the steps:

CH3-C6H4-CHO + CH3MgBr (and in a second step H2O) -> CH3-C6H4-CHOH-CH3 (and MgBrOH as side product)

CH3-C6H4-CHOH-CH3 -> CH3.C6H4-CH-CH2 + H2O (e.g. using P2O5 as dehydrating agent)

CH3.C6H4-CH-CH2 + H2 -> CH3.C6H4-CH2-CH3 (using Raney-Ni as catalyst)

The identification reaction for the aldehyde runs
CH3-C6H4-CHO + H2N-NH-C6H3-(NO2)2 ->
CH3-C6H4-CH=N-NH-C6H3-(NO2)2 + H2O

This problem ought to be solvable for a high school student after about 2 years of intensive courses in organic chemistry, with another year of general chemistry earlier. Even then, getting everything right would be closer to a test of excellence than asking basic knowledge, but a good teacher ought to be able to get his pupils to this point.

Answer 2

Clearly, for some students, Chemistry will have direct application in their careers. But in the details, I sense you're really asking why you should study it. I think the biggest reason to pursue any assignment that doesn't seem immediately relevant to a person is to learn discipline. The attitude of caring about every subject, and doing one's very best, regardless of interest level, is a success factor. For example, suppose I considered the topic of Inventory Control boring, but wanted to start a business. I'd likely get into trouble quickly. As to whether Science has all the answers, I would say no. But Science has a part in explaining why things are the way they are. If I was an investor, it would help to know what importance Tellurium has to the solar industry, and if someone came along saying they could substitute much cheaper Aluminum, remembering chemistry would help me decide whether they were full of it or not.

Answer 3

I can get a structure for A that fits (2-methyl benzaldehyde).

Now you can get on with it!

Answer 4

sorry i also have the same problem to solve