Claims:1. A process for preparing 3-methylbenzo-5,6-quinoline, said process comprising:
i. desulphonating 2-aminonaphthalene-1-sulphonic acid to obtain naphthalen-2-amine;
ii. condensing, followed by cyclizing said naphthalen-2-amine using at least one aldehyde in presence of at least one oxidizing agent and optionally diatomaceous earth to obtain a product mixture comprising 3-methylbenzo-5,6-quinoline; and
iii. separating 3-methylbenzo-5,6-quinoline from said product mixture.
2. The process as claimed in claim 1, wherein said desulphonating is performed by using sulphuric acid having concentration in the range of 50 % to 60 %.
3. The process as claimed in claim 1, wherein said aldehyde is at least one selected from the group consisting of crotonaldehyde, and paraldehyde.
4. The process as claimed in claim 1, wherein said oxidizing agent is at least one selected from the group consisting of potassium iodide, sodium iodide, potassium bromide, iodine, hydrogen iodide, hydrogen bromide, bromine, and ammonium bromide.
5. The process as claimed in claim 1, wherein said separation step involves adding water to said product mixture under stirring, followed by cooling at a temperature in the range of 20 °C to 35 °C and filtering to obtain 3-methylbenzo-5,6-quinoline.
6. The process as claimed in claim 2, wherein the molar ratio of 2-aminonaphthalene-1-sulphonic acid to sulphuric acid is in the range of 1:2.5 to 1:5.
7. The process as claimed in claim 1, wherein the molar ratio of 2-aminonaphthalene-1-sulphonic acid to aldehyde is in the range of 1:0.5 to 1:1.5.
8. The process as claimed in claim 1, wherein the molar ratio of 2-aminonaphthalene-1-sulphonic acid to oxidizing agent is in the range of 1:0.01 to 1:0.05.
9. The process as claimed in claim 1 further includes the step of purification of separated 3-methylbenzo-5,6-quinoline to obtain 3-methylbenzo-5,6-quinoline, said purification step comprises:
a. heating said 3-methylbenzo-5,6-quinoline with water at a temperature in the range of 60 °C to 80 °C to obtain a first mass;
b. filtering said first mass on a diatomaceous earth bed to collect a first filtrate, followed by adding charcoal to said first filtrate at a temperature in the range of 50 °C to 70 °C to obtain a second mass;
c. filtering said second mass on said diatomaceous earth bed to collect a second filtrate, followed by adding said second filtrate to caustic soda solution at a temperature in the range of 20 °C to 30 °C to obtain a third mass; and
d. filtering said third mass followed by washing and drying to obtain 3-methylbenzo-5,6-quinoline with yield of at least 80 % and having purity of at least 99 %.
, Description:FIELD
The present disclosure relates to a process for preparing 3-methylbenzo-5,6-quinoline.
BACKGROUND
3-methylbenzo-5,6-quinoline is also known as ß-naphthoquinaldine. 3-methylbenzo-5,6-quinoline is used for preparing naphthoquinophthalone derivatives, sulphine dyes for cotton printing. 3-methylbenzo-5,6-quinoline is also used as an agrochemical for destruction of undesired plants.
Conventionally, 2-aminonaphthalene-1-sulphonic acid (tobias acid) is heated with sulphuric acid, crotonaldehyde, and an oxidizing agent comprising nitrobenzene to obtain 3-methylbenzo-5,6-quinoline. Also, Skraup reactions can be used to prepare quinolones in which aniline or substituted aniline can be treated with glycerol, sulfuric acid, and an oxidizing agent such as nitrobenzene. In these processes, m-nitrobenzenesulfonic acid can produce metanilic acid as a by-product. The metanilic acid, which is environmentally hazardous, when released in the effluent cannot be recovered, thereby increases the environmental load.
Therefore, there is felt a need to provide an environment friendly and economical process to prepare 3-methylbenzo-5,6-quinoline.
OBJECTS
Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows.
It is an object of the present disclosure to ameliorate one or more problems of the prior art or to at least provide a useful alternative.
An object of the present disclosure is to provide an environment friendly process to prepare 3-methylbenzo-5,6-quinoline.
Another object of the present disclosure is to provide an economic process to prepare 3-methylbenzo-5,6-quinoline.
Other objects and advantages of the present disclosure will be more apparent from the following description, which is not intended to limit the scope of the present disclosure.
SUMMARY
The present disclosure relates to a process for preparing 3-methylbenzo-5,6-quinoline. The process comprises desulphonating 2-aminonaphthalene-1-sulphonic acid to obtain naphthalen-2-amine. The naphthalen-2-amine is condensed, followed by cyclizing using at least one aldehyde in presence of at least one oxidizing agent and diatomaceous earth to obtain a product mixture comprising 3-methylbenzo-5,6-quinoline. Further, 3-methylbenzo-5,6-quinoline is separated from the product mixture.

DETAILED DESCRIPTION
3-methylbenzo-5,6-quinoline can be prepared from ß-Naphthylamine or 2-aminonaphthalene-1-sulphonic acid, with condensation of crotonaldehyde or paraldehyde. In this process, m-nitrobenzenesulfonic acid can be used as an oxidizing agent that produces metanilic acid as a by-product. The metanilic acid released in effluent cannot be recovered, which increases the environmental load.
The present disclosure envisages an environment friendly and economical process for preparing 3-methylbenzo-5,6-quinoline.
In accordance with an aspect of the present disclosure there is provided a process for preparing 3-methylbenzo-5,6-quinoline. The process comprises following steps.
In the first step, 2-aminonaphthalene-1-sulphonic acid is desulphonated to obtain naphthalen-2-amine.
In accordance with an embodiment of the present disclosure, the purity of 2-aminonaphthalene-1-sulphonic acid is at least 80 %.
In accordance with one embodiment of the present disclosure, the purity of 2-aminonaphthalene-1-sulphonic acid is 97 %.
In accordance with an embodiment of the present disclosure, the desulphonation of 2-aminonaphthalene-1-sulphonic acid is performed using sulphuric acid having concentration in the range of 50 % to 60 %.
In accordance with one embodiment of the present disclosure, the concentration of sulphuric acid is 51 %.
The molar ratio of the 2-aminonaphthalene-1-sulphonic acid to sulphuric acid is in the range of 1:2.5 to 1:5.
In accordance with one embodiment of the present disclosure, the molar ratio of the 2-aminonaphthalene-1-sulphonic acid to sulphuric acid is 1:3.4.
In the second step, the naphthalen-2-amine is condensed, followed by cyclization using at least one aldehyde and at least one oxidizing agent and optionally diatomaceous earth to obtain a product mixture comprising 3-methylbenzo-5,6-quinoline.
In accordance with an embodiment of the present disclosure, the purity of the aldehyde is in the range of 80 % to 95 %. In one embodiment of the present disclosure, the purity of the aldehyde is 85 %.
In accordance with an embodiment of the present disclosure, the aldehyde is at least one selected from the group consisting of crotonaldehyde, and paraldehyde.
In one embodiment of the present disclosure, the aldehyde is crotonaldehyde.
The molar ratio of the 2-aminonaphthalene-1-sulphonic acid to the aldehyde is in the range of 1:0.5 to 1:1.5.
In one embodiment of the present disclosure, the molar ratio of the 2-aminonaphthalene-1-sulphonic acid to the crotonaldehyde is 1:1.17
In accordance with an embodiment of the present disclosure, the oxidizing agent is at least one selected from the group consisting of potassium iodide, sodium iodide, potassium bromide, iodine, hydrogen iodide, hydrogen bromide, bromine, and ammonium bromide. The use of potassium iodide used in the process of the present disclosure does not produce by-products such as metanilic acid and the like that increases environmental load when released in effluent. In accordance with an embodiment of the present disclosure, the purity of the oxidizing agent is at least 85 %. In one embodiment of the present disclosure, the purity of the oxidizing agent is 99.5 %.
In accordance with one embodiment of the present disclosure, the oxidizing agent is potassium iodide.
The molar ratio of the 2-aminonaphthalene-1-sulphonic acid to the oxidizing agent is in the range of 1:0.01 to 1:0.05.
In accordance with one embodiment of the present disclosure, the molar ratio of the 2-aminonaphthalene-1-sulphonic acid to potassium iodide is 1:0.022.
In an embodiment of the present disclosure, the diatomaceous earth prevents the powdered ingredients from sticking together. Diatomaceous earth consists of 80 % to 90 % silica, 2 % to 4 % alumina, and 0.5 % to 2 % iron oxide.
In the third step, 3-methylbenzo-5,6-quinoline is separated from the product mixture by adding water to the product mixture under stirring, followed by cooling at a temperature in the range of 20 °C to 35 °C and filtering, optionally washing and purifying to obtain 3-methylbenzo-5,6-quinoline.
Sulphuric acid having concentration in the range of 35 % to 45 % can be used for washing the product mixture comprising 3-methylbenzo-5,6-quinoline in the third step to remove soluble impurities from the product mixture.
3-methylbenzo-5,6-quinoline is purified to obtain 3-methylbenzo-5,6-quinoline having purity of at least 99 %. The purification of 3-methylbenzo-5,6-quinoline comprises heating 3-methylbenzo-5,6-quinoline with water at a temperature in the range of 60 °C to 80 °C to obtain a first mass. The first mass is filtered on diatomaceous earth bed to collect a first filtrate and charcoal is added to the first filtrate at a temperature in the range of 50 °C to 70 °C to obtain a second mass. The second mass is filtered on diatomaceous earth bed to collect a second filtrate. The second filtrate is added to caustic soda solution (25 % w/w) at a temperature in the range of 20 °C to 30 °C over a period of 1 hour to 5 hours to obtain a third mass. The reaction is exothermic and the temperature is maintained in the range of 20 °C to 30 °C by adding ice in the second filtrate. The pH of the third mass is maintained in the range of 8 to 9 by adding extra caustic soda. The third mass is stirred for 1 hour and filtered to obtain a cake. The so formed cake is washed with water till the cake is sulphate free, followed by drying the cake at a temperature in the range of 40 °C to 50 °C under reduced pressure to obtain 3-methylbenzo-5,6-quinoline with yield of at least 80 % and having purity of at least 99 %.
The reagents used in the process of the present disclosure to prepare 3-methylbenzo-5,6-quinoline are readily available and inexpensive. The process of the present disclosure does not produce environmentally hazardous by-product such as metanilic acid that increases environmental load. Therefore, the process of the present disclosure to prepare 3-methylbenzo-5,6-quinoline is environment friendly and economical.
The present disclosure is further described in light of the following experiments which are set forth for illustration purpose only and not to be construed for limiting the scope of the disclosure. The following laboratory scale experiments can be scaled up to industrial/commercial scale.
EXPERIMENTS
Experiment-1A: Preparation of 3-methylbenzo-5,6-quinoline (using potassium iodide as an oxidizing agent)
In a 2 liter flask, 600 g sulfuric acid (51%) and 208 g (97%) of 2-aminonaphthalene-1-sulphonic acid were refluxed at 130 °C for 5 hours to obtain a first mass comprising naphthalene-2-amine. Thin layer chromatography was simultaneously performed on the first mass to confirm the completion of the reaction by determining the absence of 2-aminonaphthalene-1-sulphonic acid. Further, the first mass was cooled to 100 °C, followed by adding 6 g of diatomaceous earth, and 3.3 g of potassium iodide under stirring for 30 minutes at 110 °C to obtain a second mass. Further, 87.5 g (85%) of crotonaldehyde was added over a period of 5 hours at 110 °C to obtain a product mixture, followed by heating the product mixture to 120 °C for 2 hours. Thin layer chromatography was simultaneously performed on the product mixture, comprising 3-methylbenzo-5,6-quinoline to confirm the completion of the reaction by determining the absence of ß-Naphthylamine. The temperature of the product mixture was reduced to 90 °C, followed by adding 356 ml of water to the product mixture. The product mixture was cooled to 30 °C to obtain a suspension. The so formed suspension was filtered to obtain a cake comprising 3-methylbenzo-5,6-quinoline. The cake was washed with 150 ml (40% w/w) of sulphuric acid to obtain 385 g of 3-methylbenzo-5,6-quinoline having 3 % moisture content.
Experiment-1B: Purification of 3-methylbenzo-5,6-quinoline (obtained in experiment-1A of the present disclosure)
In a 2 liter flask, 1100 ml of water and 385 g of 3-methylbenzo-5,6-quinoline obtained in experiment-1A of the present disclosure were heated at 80 °C for 1 hour to obtain a first mass. The so formed first mass was filtered on a diatomaceous earth bed and a first filtrate was collected. The so formed first filtrate was added to a flask, followed by adding 3 g of charcoal and the flask was heated at 60 °C for 1 hour to obtain a second mass. The so formed second mass was filtered on a diatomaceous earth bed and collected a second filtrate. Further, 400 g of caustic soda solution (25% w/w) was charged in a 5 liter bucket, followed by slowly adding the second filtrate over a period of 3 hours at 25 °C to obtain a third mass. The reaction was exothermic and the temperature of the bucket was maintained at 25 °C by adding 800 g of ice. The pH of the third mass was maintained at 8 by adding extra caustic soda. The third mass was stirred for 1 hour and filtered to obtain a cake. The so formed cake was washed with water till the cake was sulphate free, followed by drying the cake at 45 °C under reduced pressure to obtain 155 g of 3-methylbenzo-5,6-quinoline (Purity = 99.8 %, Melting point = 80 °C).
The chemical oxygen demand (COD) for filtrate of 3-methyl-5,6-quinoline experiment-1A was found to be 19700 mg/liter.
Comparative experiment-2A: Preparation of 3-methylbenzo-5,6-quinoline (using m-nitrobenzenesulphonic acid sodium salt as an oxidizing agent)
In a 2 liter flask, 600 g sulfuric acid (51%) and 208 g (97%) of 2-aminonaphthalene-1-sulphonic acid were refluxed at 130 °C for 5 hours to obtain a first mass comprising naphthalene-2-amine. Thin layer chromatography was simultaneously performed on the first mass to confirm the completion of the reaction by determining the absence of 2-aminonaphthalene-1-sulphonic acid. Further, the first mass was cooled to 100 °C, followed by adding 6 g of diatomaceous earth, 0.03 g of ammonium meta vanadate, and 75.5 g of m-nitrobenzenesulphonic acid sodium salt under stirring for 30 minutes & heat to 110 °C to obtain a second mass. Further, 87.5 g (85%) of crotonaldehyde was added over a period of 5 hours at 110 °C to obtain a product mixture followed by heating the product mixture to 120 °C for 2 hours. Thin layer chromatography was simultaneously performed on the product mixture, comprising 3-methylbenzo-5,6-quinoline to confirm the completion of the reaction by determining the absence of ß-Naphthylamine. The temperature of the product mixture was reduced to 90 °C, followed by adding 356 ml of water to the product mixture. The product mixture was cooled to 30 °C to obtain a suspension. The so formed suspension was filtered to obtain a cake comprising 3-methylbenzo-5,6-quinoline. The cake was washed with 450 ml (40% w/w) of sulphuric acid to obtain 341 g of 3-methylbenzo-5,6-quinoline having 3 % moisture content.

Comparative experiment-2B: Purification of 3-methylbenzo-5,6-quinoline (obtained in experiment-2A of the present disclosure)
The process for the purification of 3-methyl-5,6-quinoline obtained in comparative experiment-2A was similar to experiment-1B of the present disclosure. The yield of 3-methylbenzo-5,6-quinoline obtained by the process of comparative experiment-2A was 136 g (Purity = 99.5 %, Melting point = 79 °C).
The chemical oxygen demand (COD) for filtrate of 3-methyl-5,6-quinoline obtained by comparative experiment-2A was found to be 74000 mg/liter.
It is evident from the above experiments that the chemical oxygen demand of FILTRATE OF 3-methyl-5,6-quinoline obtained by experiment-1A is less compared to FILTRATE OF 3-methyl-5,6-quinoline obtained by comparative experiment-2A. Also, the reagents used in the process of the present disclosure to prepare 3-methylbenzo-5,6-quinoline are readily available and inexpensive. Therefore, the process of the present disclosure to prepare 3-methylbenzo-5,6-quinoline is environment friendly, and economical.
TECHNICAL ADVANCES AND ECONOMICAL SIGNIFICANCE
The process of the present disclosure described herein above has several technical advantages including, but not limited to, the realization of a process for preparing 3-methylbenzo-5,6-quinoline that is
? an environment friendly; and
? an economical.
The foregoing description of the specific embodiments so fully reveals the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.
Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
The use of the expression “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the invention to achieve one or more of the desired objects or results. While certain embodiments of the inventions have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Variations or modifications to the formulation of this invention, within the scope of the invention, may occur to those skilled in the art upon reviewing the disclosure herein. Such variations or modifications are well within the spirit of this invention.
The numerical values given for various physical parameters, dimensions and quantities are only approximate values and it is envisaged that the values higher than the numerical value assigned to the physical parameters, dimensions and quantities fall within the scope of the invention unless there is a statement in the specification to the contrary.
While considerable emphasis has been placed herein on the specific features of the preferred embodiment, it will be appreciated that many additional features can be added and that many changes can be made in the preferred embodiment without departing from the principles of the disclosure. These and other changes in the preferred embodiment of the disclosure will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation.