CROSS-REFERENCE TO RELATED APPLICATIONS AND PRIORITY

The present application claims priority from Indian provisional patent application number 202221028146 filed on 17 May 2022, incorporated herein by a reference.

TECHNICAL FIELD

The present subject matter described herein, in general, relates to a process of preparation of 3- Hydroxy Benzo-trifluoride alternatively known as Meta-Hydroxy Benzo-trifluoride (MHBTF). In particular, the present subject matter is related to the preparation of highly pure meta-hydroxy benzo- trifluoride (MHBTF) with improved yield.

BACKGROUND

3-Hydroxy Benzo-trifluoride or Meta-Hydroxy Benzo-trifluoride (hereinafter alternatively referred as “3- HBTF” or “MHBTF”) is colourless to pale yellow liquid used as an intermediate for the synthesis of agrochemical compounds such as herbicides.

In state of the art, CN101781174B discloses a method for synthesizing m-trifluoromethyl phenol by diazotization of 3 -Trifluoromethylaniline in presence of urea followed by hydrolysis and steam distillation.

In state of the art, CN106916052A discloses a kind of preparation method of m-trifluoromethyl phenol. The said method involves reaction of amido benzotrifluoride with sodium nitrite as a diazotization reagent in presence of 98% sulfuric acid. In state of the art, CN111559959A discloses a method of synthesizing p-trifluoromethyl phenol. The said method involved diazotization reaction between P-trifluoromethylaniline, strong acid type cation exchange resin, and sodium nitrite.

In state of the art, the conventional processes of preparing MHBTF lack in many aspects such as lower yield, loss of product, loss of reactants, high amount of impurities, and effluent recovery, etc.

Therefore, there is a long felt need of developing an economic process for preparing Meta-Hydroxy Benzo-trifluoride product by utilizing a different reaction route with different reaction conditions, minimizing the reactants consumption, minimizing the loss of reactants and thereby increasing the overall purity and yield of Meta-Hydroxy Benzo-trifluoride (MHBTF). Also, there is also a long felt need of implementing recovery and reuse of spent acid and other solvents used in the MHBTF preparation process mode to achieve environmental effectiveness and cost efficiency.

SUMMARY

Before the present system and its components are described, it is to be understood that this disclosure is not limited to the particular system and its arrangement as described, as there can be multiple possible embodiments which are not expressly illustrated in the present disclosure. This summary is provided to introduce concepts related to a preparation method of Meta-Hydroxy Benzo-trifluoride (MHBTF). This summary is not intended to identify essential features of the claimed subject matter nor is it intended for use in detecting or limiting the scope of the claimed subject matter.

As disclosed herein the present subject matter provides, a process of preparing Meta-Hydroxy Benzo- trifluoride (MHBTF) is disclosed herein. The process of preparation of Meta-Hydroxy Benzo- trifluoride (MHBTF) may comprise various one or more steps.

In one embodiment, the process may comprise a step of reaction of sulfuric acid (H2SO4) with 3- aminobenzotrifluoride at 30-55 °C to obtain a reaction mass. The process may comprise a step of diazotization of the reaction mass in presence of nitrosyl sulfuric acid (NS A) to obtain a diazotized sulphate salt of 3 -aminobenzotrifluoride. The process may comprise a step of removing excess nitrogen oxides (NOx) from the mixture by treating the diazotized sulphate salt of 3- aminobenzotrifluride with sulfamic acid. The process may comprise a step of hydrolysis of the diazotized sulfate salt of 3 -aminobenzotrifluride in presence of toluene at a temperature of 70-90 °C to obtain a crude meta hydroxy benzo-trifluoride. The process may comprise a step of layer separation of crude meta hydroxy benzotrifluoride in an organic layer from aqueous layer. The process may comprise a step of distillation of the organic layer to obtain meta hydroxybenzotrifluoride, wherein meta hydroxy benzotrifluoride (MHBTF) of high yield between 98-99% and high purity of 99.1- 99.9% is obtained.

List of Abbreviations

MHBTF - Meta-Hydroxy Benzo-trifluoride

3-HBTF- 3-Hydroxy Benzo-trifluoride

3-ABTF - 3 -aminobenzotrifluoride

NSA- Nitrosyl sulfuric acid

NOX- nitro-o-xylene

BRIEF DESCRIPTION OF FIGURES

The detailed description is described with reference to the accompanying Figures. In the Figures, the left-most digit(s) of a reference number identifies the Figure in which the reference number first appears. The same numbers are used throughout the drawings to refer like features and components.

Figure 1 depicts a process (100) of preparing a Meta-Hydroxy Benzo-trifluoride (MHBTF) in accordance with an embodiment of the present subject matter.

DETAILED DESCRIPTION

Reference throughout the specification to “various embodiments,” “some embodiments,” “one embodiment,” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, appearances of the phrases “in various embodiments,” “in some embodiments,” “in one embodiment,” or “in an embodiment” in places throughout the specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments.

The words "comprising," "having," "containing," and "including," and other forms thereof, are intended to be equivalent in meaning and be open ended in that an item or items following any one of these words is not meant to be an exhaustive listing of such item or items or meant to be limited to only the listed item or items.

It must also be noted that, the singular forms "a," "an," and "the" include plural references unless the context clearly dictates otherwise. Although any methods similar or equivalent to those described herein can be used in the practice or testing of embodiments of the present disclosure, the exemplary methods are described. The disclosed embodiments are merely exemplary of the disclosure, which may be embodied in various forms.

Various modifications to the embodiment may be readily apparent to those skilled in the art and the generic principles herein may be applied to other embodiments. However, one of ordinary skill in the art may readily recognize that the present disclosure is not intended to be limited to the embodiments illustrated but is to be accorded the widest scope consistent with the principles and features described herein. The detailed description of the invention will be described hereinafter referring to accompanied drawings.

In one embodiment of the present invention, Meta-Hydroxy Benzo-trifluoride (MHBTF) maybe alternatively referred to as 3-Hydroxy Benzo-trifluoride.

In one embodiment of the present invention, referring figure 1, a process (100) for preparing a MetaHydroxy Benzo-trifluoride (MHBTF) is illustrated in accordance with the embodiments of the present invention. The process (100) of preparation of Meta-Hydroxy Benzo-trifluoride (MHBTF) comprises of various steps and further divided into three stages.

In one embodiment of the present invention, the process (100) may comprise a first stage (stage A) of diazotization of 3-aminobenzotrifluoride (3-ABTF) to obtain a diazotized sulfate salt. The said process further may comprise a second stage (stage B) of hydrolysis of the said diazotized sulfate salt of 3-aminobenzotrifluoride obtained in first stage to obtain Meta-Hydroxy benzo-trifluoride (MHBTF). The stage B further may comprise of recovery and recycle of spent acid effluent such as sulfuric acid spent. The said process further may comprise a third stage (stage C) of distillation of organic layer to obtain pure meta-hydroxy benzo-trifluoride. In one embodiment, the overall process is preferably performed in a batch mode.

A first stage of diazotization of 3-aminobenzotrifluoride (3-ABTF) - Stage (A)

In one embodiment of the present invention, referring to figure 1, the process (100) may include a first stage of diazotization (Stage A) of 3-aminobenzotrifluoride (3-ABTF) to obtain a diazotized sulfate salt. The process (100) may comprise a step of reaction (101) of sulfuric acid (H2SO4) with 3- aminobenzotrifluoride at 30-55 °C to obtain a reaction mass. The step of reaction of sulfuric acid (H2SO4) with 3- aminobenzotrifluoride may further comprise a sub-step of cooling the said reaction mass to a predetermined temperature range between 0-28 °C.

Further, the process may comprise step of diazotization (105) of the reaction mass in presence of nitrosyl sulfuric acid (NSA) to obtain a diazotized sulphate salt of 3-aminobenzotrifluoride. The diazotization reagent may be selected from diazotization reagents including but not limited to nitrosyl sulfuric acid (NSA). Stage: 1 Diazotization:

3-ABTF NSA Sulfuric acid Diazo Water

Further, the process (100) may comprise a step of removing (107) excess nitrogen oxides (NOx) from the reaction mixture by treating the diazotized sulphate salt of 3 -aminobenzotrifluride with sulfamic acid. The treatment of sulfamic acid is carried out to remove excess NOx gas content from the said diazotized sulfate salt of 3 -aminobenzotrifluoride and thereby increasing the overall MHBTF reaction yield to more than 98%. In one embodiment of the present invention, the sulfamic acid may be used in a molar ratio between 0.01-0.1 to remove excess NOx and form a diazotized 3- aminobenzotrifluoride product obtained at the diazotization stage.

It is observed that the higher concentration of sulfuric acid increases the stability of diazo compound but decreases the rate of reaction of hydrolysis, therefore 40-50 % of sulfuric acid may be used in first step of stage (A).

It is observed that the yield of diazotized sulfate salt of 3-amino hydroxy benzo-trifluoride is less to 72.6% if sodium nitrite is used instead of the said nitrosyl sulfuric acid (NSA) as a diazotizing reagent. Therefore, in a preferred embodiment a 30-40 % nitrosyl sulfuric acid (NSA) may be used, more preferably 36-37% nitrosyl sulfuric acid (NSA) is used.

It is observed that in the present invention, reactants 3-aminobenzotrifluoride (3-ABTF), Sulfuric acid (H2SO4), and nitrosyl sulfuric acid (NSA) may be incorporated in a molar ratio of 0.5-2:2-7:0.5-2, and preferably 1 :4.29: 1.05 respectively. The process (100), wherein one mole of sulfuric acid is used for diazotized salt solution and the additional rest content of sulfuric acid in the reaction increases the flowability of the diazotized salt solution, less mole of sulfuric acid leads to thick and non-flowable slurry. The concentration of sulfuric acid impacts on stability of diazo product but also may affect and decrease the rate of reaction of hydrolysis. Therefore, preferably a 40-50% Sulfuric acid concentration is considered optimum to get better yield diazo product and better conversion.

The higher concentration of sulfuric acid enables improvement and increase in stability of diazo mass that eventually leads yield improvement of final MHBTF product. Due to increase in diazo mass throughput, the bottom residue obtained after distillation is minimum, when the process (100) is implemented.

A second stage of hydrolysis of the diazotized sulfate salt of 3-aminobenzotrifluoride to obtain metahydroxy benzo-trifluoride (MHBTF)- Stage (B) In yet another embodiment of the present invention, the process (100) may comprise a second stage (B) of hydrolysis of the said diazotized sulfate salt of 3 -aminobenzotrifluoride to obtain MetaHydroxy benzo-trifluoride (MHBTF). The process (100) may comprise hydrolysis (109) of the diazotized sulfate salt of 3 -aminobenzotrifluride in presence of toluene at a temperature of 70-90 °C to obtain a crude meta hydroxy benzo-trifluoride.

Stage: 2 Hydrolysis:

Diazo Water MHBTF Nitrogen gas Sulfuric acid

In another embodiment of the present invention, at a step of hydrolyzing (109) the said diazotized sulfate salt of 3 -aminobenzotrifluoride in the presence of toluene the predetermined temperature may be maintained between 70-90 °C, and preferably between 85-90 °C.

In still another embodiment of the present invention, the process (100) may comprise a step of recovery of spent acid effluent such as sulfuric acid spent after hydrolysis of the diazotized salt. The sulfuric acid spent in the first stage may be recycled multiple times in the process (100).

The recovery of spent acid effluent from the hydrolysis (109) step is enabled upto 50-60%, and more preferably 53-55% of spent acid effluent recovery of spent acid effluent, and thereby achieving minimal liquid discharge of effluents.

The process (100) may further comprise a step of layer separation (111) of crude meta hydroxy benzotrifluoride in an organic layer from aqueous layer. The step of layer separation (111) may further comprise separating the organic layer from aqueous layer and alkali washing the said organic layer with ammonia, calcium hydroxide, sodium bicarbonate and sodium hydroxide (NaOH) and preferably sodium carbonate (ISfeCCh).

A third stage of distillation of organic layer to obtain meta hydroxybenzotrifl uoride. (MHBTF) - Stage (Q

In the next stage (C), distillation (113) of the organic layer to obtain meta hydroxybenzotrifluoride is performed, wherein meta hydroxy benzotrifluoride (MHBTF) of high yield between 98-99% and high purity of 99.1-99.9% is obtained.

In another embodiment of the present invention, at a step of distillation (113) is preferably a fractional distillation. In one embodiment of the present invention, the purity of the Meta-Hydroxy benzo-trifluoride (MHBTF) obtained by said process (100) may be between 99-99.9%.

In one embodiment of the present invention, the yield of the Meta-Hydroxy benzo-trifluoride (MHBTF) obtained by said process (100) may be between 98-99%.

In accordance with the preferred embodiment of the present disclosure, a batch process is followed for preparation of meta-Hydroxy Benzo- trifluoride (MHBTF). In one embodiment of the present disclosure, the said batch process may comprise diazotization of 3 -aminobenzotrifluoride (3-ABTF) to obtain a diazotized sulfate salt. Further, 3 -aminobenzotrifluride reacts with sulfuric acid at 30-55 °C to obtain a reaction mass, wherein the reaction mass is cooled down at 25-28 °C. The sulfuric acid added is 40-50%. Further the diazotizing reagent 36.5% nitrosyl sulfuric acid (NSA) may be added to reaction to form a diazotized salt of 3 -aminobenzotrifluride. The diazotized salt of 3- aminobenzotrifluride may be further treated with sulfamic acid in a molar ratio between 0.01-0.1 to remove undesired nitrogen oxides (NOx) gases from diazotized 3 -aminobenzotrifluoride.

The as disclosed method steps enable increment in overall yield of the final product. The 3- aminobenzotrifluoride, sulfuric acid, and nitrosyl sulfuric acid (NSA) are incorporated in a molar ratio of 0.5-2:2-7:0.5-2.

The said process further follows a step of hydrolysis of the said diazotized sulfate salt of 3- aminobenzotrifluoride in presence of toluene at 70-90°C to obtain crude Meta-Hydroxy benzo - trifluoride (MHBTF). The process may further comprise a step of recovery of acid spent sulfuric acid by 53-55% from the reaction mass after the step of hydrolysis. The recovery of sulfuric acid spent is adjusted such that yield increment is unaffected. The spent acid concentration above specified range may lead to issue with diazotization and can discompose and form HF which is undersired.

The crude meta-hydroxy benzo-trifluoride is then separated into an organic layer from an aqueous layer by alkali washing the organic layer with sodium carbonate (Na2CO3). Further, there is fractional distillation of the organic layer to obtain pure meta hydroxyl benzo trifluoride (MHBTF).

In one embodiment, the disclosed is a pure meta hydroxyl benzo trifluoride (MHBTF) having appearance as clear colorless to pale yellow liquid, wherein a purity of the meta hydroxyl benzo trifluoride (MHBTF) product obtained by the said process (100) is 99.1-99.9%, and wherein the MHBTF may comprise 3 -Amino benzotrifluoride no more than 0.2%, and moisture content no more than 0.2%.

The following experiments further illustrate the invention. All parts and percentages are by weight unless explicitly stated otherwise.

EXAMPLES

Example 1: Preparation of MHBTF by NaNCh (Batch mode) 10.65 moles 50-55% sulfuric acid, and 2.48 moles 3-amino BTF at 30-40 °C was added to the reactor to obtain a reaction mass. The reaction mass was cooled to 25-30 °C. Further, 2.61 moles 40% sodium nitrite was added to a solution for diazotization. The diazotized reaction mass was maintained for Ihr. In another reactor 3.17 parts/volume toluene was taken. The toluene was further heated to 80-85 °C. Added diazo mass for Hydrolysis at same temperature. After addition of diazo mass to the second reactor, the reaction was maintained for 1 hr, followed by cooling the reaction mass for layer separation and work up. The organic layer was separated from aqueous layer and neutralized. The neutralized organic layer was treated for toluene recovery and product distillation. Yield was 72-73% and Purity was 99.5-99.7%.

Example 2: method for preparation of meta-hydroxy benzo-trifluoride using nitroso sulfuric acid (NSA) as a diazotizing agent -Batch mode

10.65 Kmoles of 60-65% sulfuric acid was taken in reactor. 2.48 Kmoles of 3-amino BTF were added at temperature 30-40°C to obtain a reaction mixture. The reaction mixture was then cooled to 25- 30°C. Further, 2.61 Kmoles 35%-37% Nitrosyl sulfuric acid was added to the reaction mixture as a diazotization reagent. The reaction was maintained for IHr for diazotization to obtain diazotized amino BTF. 20% of sulfamic acid was added to the reaction mass comprising diazotized amino BTF to kill excess nitrosyl sulfuric acid and to remove NOx from the reaction mixture. In another reactor, 3.17 parts by volume toluene was taken and heated to 80-85 °C. Further, a diazotized amino BTF mass was added to the reactor for hydrolysis at same temperature. After addition of diazotized amino BTF, the reaction mass was maintained for IHr and cooled down further for layer separation and workup. The neutralized organic layer was treated for toluene recovery and product distillation. Yield was 82-87% and Purity was 99.6-99.8%.

Example 3: method for preparation of meta-hydroxy benzo-trifluoride using nitroso sulfuric acid (NSA) as a diazotizing agent -Batch mode

10.65 Kmoles 15-20% sulfuric acid was taken in a reactor. Further, 2.48 Kmoles 3-amino BTF were added at temperature 30-40 °C to obtain a reaction mixture. The reaction mixture was then cooled to 25-30°C. In the next step, 2.61 Kmoles 35%-37% Nitrosyl sulfuric acid was added to the reaction mixture as a diazotization reagent. The reaction mixture was maintained for IHr for diazotization to obtain diazotized amino BTF. Further, 20% of sulfamic acid was added to the reaction mass comprising diazotized amino BTF to kill excess nitrosyl sulfuric acid and to remove excess NOx from the reaction mixture. In another reactor 3.17 parts by volume of toluene was taken and heated to SO- 85 °C. Further, a diazotized amino BTF mass was added to the reactor for hydrolysis at same temperature. After addition of diazotized amino BTF, the reaction mass was maintained for IHr and cooled down further for layer separation and work up. The neutralized organic layer was treated for toluene recovery and product distillation. Yield was 75-80% and Purity was 99.5-99.7%.

Example 4: method for preparation of meta-hydroxy benzo-trifluoride using nitroso sulfuric acid as a diazotizing agent (NSA) -Batch mode

10.65 Kmoles of 50-55% sulfuric acid was taken in reactor. 2.48 Kmoles of 3-amino BTF were added at temperature 30-40 °C to obtain a reaction mixture. The reaction mixture was then cooled to 25-30 °C. 2.61 Kmoles, and 35%-37% Nitrosyl sulfuric acid was added to the reaction mixture as a diazotization reagent. The reaction was maintained for IHr for diazotization to obtain diazotized amino BTF. Further, 20% of sulfamic acid was added to the reaction mass comprising diazotized amino BTF to kill excess nitrosyl sulfuric acid and to remove NOx from the reaction mixture. In another reactor 3.17 parts by volume toluene was taken and heated to 80-85 °C. Further, a diazotized amino BTF mass was added to the reactor for hydrolysis at same temperature. After addition of diazotized amino BTF, the reaction mass was maintained for IHr and cooled down further for layer separation and work up. The neutralized organic layer was treated for toluene recovery and product distillation. Yield was 80-85% and Purity was 99.7-99.95%.

Example 5: A method for preparation of meta-hydroxy benzo-trifluoride using nitroso sulfuric acid as a diazotizing agent (NSA) -Batch mode

10.65 Kmoles of 40-50% of sulfuric acid was added in a reactor. Further, 2.48 Kmoles (16.17%) 3- Amino BTF at 30-40 °C to obtain a reaction mixture. The reaction mixture was then cooled to 25-30 °C. Further, 2.61 Kmoles 35%-37% Nitrosyl sulfuric acid was added to the reaction mixture as a diazotization reagent, and the reaction mixture was maintained for IHr. Further, 20% sulfamic acid was added in the reaction mixture to kill excess Nitrosyl sulfuric acid and other NOx components. 80% content of sulfamic acid solution was comprising of water. In another reactor, about 3.17 parts by volume Toluene was added and heated up to 80-85 °C. The diazotized mass was added to the reactor for hydrolysis at same temperature. After addition of diazotized mass in a reactor, the reaction was maintained for Ihr and further cooled for layer separation and work up. The neutralized organic layer was treated for toluene recovery and product distillation. Yield was 98-99% and Purity was 99.95%.

Example 6: Recovery and reuse of sulfuric acid from MHBTF preparation process

Referring to previous Examples 2-5, after step of hydrolysis, a % recovery of 50-60% spent acid effluent having strength 50-55%, and more preferably 53-55% of reusable sulfuric acid is carried out, and thereby achieving minimal liquid discharge of effluents. The recycled effluent from the primary process (100) can then be reused in the preparation of MHBTF as per below examples 7A-7C. Example 7A: A method of preparation of MHBTF by using recovered sulfuric acid from Examples 2-5

10.65 Kmoles spent sulfuric acid diluted to 40-50% (1st recycle of spent from example no: 6) was taken in a reactor. Further, 2.48 Kmoles 3-Amino BTF was added to the reactor at temperature 30-40 °C to obtain a reaction mass. The reaction mass was then cooled to 25-30 °C. Further, 2.61 Kmoles of 35%-37% Nitrosyl sulfuric acid was added to the reaction mixture as a diazotization reagent and the reaction was maintained for Ihr. Further, 20% sulfamic acid was added to the recti on mixture to kill excess Nitrosyl sulfuric acid, where the remaining 80% of sulfuric acid solution was water. In another reactor about 3.17 parts by volume of Toluene was added and heated upto 80-85 °C. Further, the diazo mass of Amino BTF was added to the reactor comprising heated toluene for Hydrolysis at same temperature. After addition diazo mass of Amino BTF to the reaction mixture, the reaction was maintained for Ihr and cooled the mass for layer separation and work up. The neutralized organic layer was treated for toluene recovery and product distillation. Yield was 98-99% and Purity was 99.6-99.9%.

Example 7B: A method of preparation of MHBTF by using recovered sulfuric acid from Examples 2-5

10.65 Kmoles of spent sulfuric acid diluted to 40-50% (2 ^nd recycle of spent from example no: 6) was taken in a reactor. Further 2.48 Kmoles 3-Amino BTF was added to the reactor at temperature of 30- 40 °C to obtain a reaction mixture. The reaction mixture was then cooled to 25-30 °C and 2.61 Kmoles 35%-37% nitrosyl sulfuric acid was added to the reaction mixture as a diazotization reagent. The reaction mixture was maintained for Ihr to obtain diazotized 3-Amino BTF. Further, 20% sulfamic acid was added to kill excess Nitrosyl sulfuric acid and NOx. In another reactor 3.17 parts by volume toluene was taken and heated up to 80-85 °C. The diazotized 3-Amino BTF mass was then put through hydrolysis at same temperature. After addition of diazotized 3-Amino BTF mass maintained for Ihr and cooled for layer separation and work up. Neutralized organic layer and sent for Toluene recovery and product distillation. Yield was 98-99% and Purity was 99.6-99.9%.

Example 7C: A method for recovery of sulfuric acid in the MHBTF preparation process of Examples 2-5

10.65 Kmoles of spent sulfuric acid diluted to 40-50% (3rd recycle of spent from example no: 6) was taken in a reactor. Further 2.48 Kmoles 3-Amino BTF was added to the reactor at temperature of 30- 40 °C to obtain a reaction mixture. The reaction mixture was then cooled to 25-30 °C and 2.61 Kmoles 35%-37% nitrosyl sulfuric acid was added to the reaction mixture as a diazotization reagent. The reaction mixture was maintained for Ihr to obtain diazotized 3-Amino BTF. Further, 20% sulfamic acid was added to kill excess Nitrosyl sulfuric acid and NOx. In another reactor 3.17 parts by volume toluene was taken and heated up to 80-85 °C. The diazotized 3-Amino BTF mass was then put through hydrolysis at same temperature. After addition of diazotized 3-Amino BTF mass maintained for Ihr and cooled for layer separation and work up. Neutralized organic layer and sent for Toluene recovery and product distillation. Yield was 98-99% and Purity was 99.6-99.9%. In accordance with embodiment of the present disclosure, the process (100) of preparing MetaHydroxy benzo-trifluoride (MHBTF) described above have following advantages including but not limited to:

• Increasing the final yield of Meta-Hydroxy benzo-trifluoride (MHBTF) up to 99%.

• Increase in the purity of Meta-Hydroxy benzo-trifluoride (MHBTF) up to 99.9%. • Reduction in loss of reactants such as sulfuric acid (H2SO4) by recycling.

• Removal of excess of NOx gases from the reaction mixture thereby improving MHBTF yield.

• Increase in the concentration of sulfuric acid leads to increase in diazo compound and the concentration of yield is increased and the reduction of bottom residue achieved after distillation. The embodiments, examples and alternatives of the preceding paragraphs or the description and drawings, including any of their various aspects or respective individual features, may be taken independently or in any combination. Features described in connection with one embodiment are applicable to all embodiments, unless such features are incompatible.