The Production Process of 6-Methoxyquinoline-3-carboxylic acid

6-Methoxyquinoline-3-carboxylic acid is an important intermediate in the production of various pharmaceuticals, agrochemicals, and other chemical products.
The production process of 6-methoxyquinoline-3-carboxylic acid involves several steps, which can be divided into two main stages: the synthesis of 6-methoxyquinoline-3-ol and the esterification of 6-methoxyquinoline-3-ol with carboxylic acids.

Synthesis of 6-methoxyquinoline-3-ol:
The synthesis of 6-methoxyquinoline-3-ol involves a multi-step process that involves several chemical reactions.
The synthesis can be carried out using either of the two methods, which are the classical method or the modern microbiological method.

The classical method involves the following steps:

1. Preparation of 3-methylquinoline-2-carboxylate: This is done by treating 3-methylquinoline with carbon dioxide in the presence of a strong acid, such as sulfuric acid.
   
2. Reduction of 3-methylquinoline-2-carboxylate: This is done by reducing 3-methylquinoline-2-carboxylate with lithium aluminum hydride (LiAlH4) in the presence of a solvent, such as ether or tetrahydrofuran.
   
3. Dehydrogenation of the resulting 3-methylquinoline: This is done by treating 3-methylquinoline with a reducing agent, such as lithium metal in a solvent, such as THF.
   
4. Oxidation of the resulting 6-methoxy-α-tetralone: This is done by treating 6-methoxy-α-tetralone with potassium permanganate in a solvent, such as methanol.
   
5. Dehydroxylation of 6-methoxy-α-tetralone: This is done by treating 6-methoxy-α-tetralone with a dehydroxylating agent, such as sodium hydroxide or potassium hydroxide, in a solvent, such as ethanol.
   

The modern microbiological method involves the following steps:

1. Preparation of 3-methylquinoline-2-carboxylate: This is done by fermenting 3-methylquinoline using a microorganism, such as Escherichia coli or Bacillus subtilis.
   
2. Reduction of 3-methylquinoline-2-carboxylate: This is done by reducing 3-methylquinoline-2-carboxylate with a reducing agent, such as hydrogen gas or lithium aluminum hydride (LiAlH4), in the presence of a solvent, such as ether or tetrahydrofuran.
   
3. Dehydrogenation of the resulting 3-methylquinoline: This is done by treating 3-methylquinoline with a reducing agent, such as lithium metal in a solvent, such as THF.
   
4. Oxidation of the resulting 6-methoxy-α-tetralone: This is done by treating 6-methoxy-α-tetralone with potassium permanganate in a solvent, such as methanol.
   
5. Dehydroxylation of 6-methoxy-α-tetralone: This is done by treating 6-methoxy-α-tetralone with a dehydroxylating agent, such as sodium hydroxide or potassium hydroxide, in a solvent, such as ethanol.
   

Esterification of 6-methoxyquinoline-3-ol with carboxylic acids:
The ester