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Title:
A PROCESS FOR SELECTIVE OXIDATION OF ORTHO-CRESOL AND CATALYST THEREOF
Document Type and Number:
WIPO Patent Application WO/2021/024275
Kind Code:
A1
Abstract:
The present invention relates to process for selective oxidation of o-cresol using heterogeneous catalyst. More particularly, the present invention relates to a selectively salicylaldehyde by oxidation of o-cresol, comprising steps of treating o-cresol with heterogeneous catalyst consisting of 3-7 % cobalt doped octahedral molecular sieves (OMS-2) support having Surface area between 80- 140 m2/g and pore size between 5 to 20 nm, the treatment is in presence of methanol and molecular oxygen at temperature between 60-85°C and pressure between 3 to 5 atm for time between 1 to 2 h. The process of present invention is to achieve high yield and conversion at mild reaction conditions.

Inventors:
YADAV GANAPATI DADASAHEB (IN)
PISAL DEVENDRA SHRIRAM (IN)
Application Number:
IN2020/050692
Publication Date:
February 11, 2021
Filing Date:
August 05, 2020
Export Citation:
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Assignee:
YADAV GANAPATI DADASAHEB (IN)
International Classes:
C07C2/30; B01J35/10
Other References:
C. LIANG ET AL.: "Magnetic nanostructured cobalt-cobalt oxide/nitrogen-doped carbon material as an efficient catalyst for aerobic oxidation of p-cresols", MOL. CATAL ., vol. 453, no. 2018, July 2018 (2018-07-01), pages 121 - 131, XP055790899, DOI: 10.1016/j.mcat.2018.05.005
F. WANG ET AL.: "Oxidation of pCresol to pHydroxybenzaldehyde with Molecular Oxygen in the Presence of CuMnOxide Heterogeneous Catalyst", ADVANCED SYNTHESIS & CATALYSIS, vol. 346, no. 6, May 2004 (2004-05-01), pages 633 - 638, XP055790902, DOI: 10.1002/adsc.200303226
S. YUANBIN ET AL.: "Oxidation of p/o-Cresols to p/o-Hydroxybenzaldehydes Catalyzed by Metalloporphyrins with Molecular Oxygen", CHINESE JOURNAL OF CHEMICAL ENGINEERING, vol. 20, no. 2, 1 April 2012 (2012-04-01), pages 262 - 266, XP055790906
Attorney, Agent or Firm:
THAKARE, Tanuja Nandkumar (IN)
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Claims:
CLAIMS Claim,

1. A process for production of selectively salicylaldehyde by oxidation of o- cresol, comprising steps of treating o-cresol with heterogeneous catalyst in presence of methanol and molecular oxygen at temperature between 60-

85°C and pressure between 3 to 5 atm for time between 1 to 2 h.

2. The process for production of selectively salicylaldehyde by oxidation of o- cresol as claimed in claim 1, wherein reaction temperature is between 70- 80 °C for time between 1 to 2 hr. 3. The process for selectively salicylaldehyde by oxidation of o-cresol as claimed in claim 1, wherein catalyst is selected from 3-7 % cobalt doped octahedral molecular sieves (OMS-2) support.

4. The process for selectively salicylaldehyde by oxidation of o-cresol as claimed in claim 3, wherein catalyst is having Surface area between 80- 140 m2/g and pore size between 5 to 20 nm.

5. The process for selectively salicylaldehyde by oxidation of o-cresol as claimed in claim 1, wherein catalyst concentration is between 0.008 to 0.013 wt. %.

1

Description:
TITLE OF THE INVENTION:

A PROCESS FOR SELECTIVE OXIDATION OF o/Vio-C RESOL AND CATALYST THEREOF FIELD OF INVENTION

The present invention relates to process for selective oxidation of o-cresol using heterogeneous catalyst. More particularly, the present invention relates to a selectively salicylaldehyde by oxidation of o-cresol, comprising steps of treating o- cresol with heterogeneous catalyst consisting of 3-7 % cobalt doped octahedral molecular sieves (OMS-2) support having Surface area between 80- 140 m 2 /g and pore size between 5 to 20 nm, the treatment is in presence of methanol and molecular oxygen at temperature between 60-85°C and pressure between 3 to 5 atm for time between 1 to 2 h. The process of present invention is to achieve high yield and conversion at mild reaction conditions.

BACKGROUND OF THE INVENTION

2-Hydroxy-benzaldehydes (HBAL) also known as salicylaldehyde (SAL) is one of the industrially important chemicals, found as the major product in the oxidation of o-cresol.

General oxidation reaction of o-cresol is depicted in Reaction scheme I.

°- creso1 salicyl aldehyde (SAL) salicylic acid (SAC) salicyl alcohol (SA)

Reaction scheme I

Salicylaldehyde (SAL) is well-known chemical intermediate and represents major platform molecule for variety of applications such as in the synthesis of pharmaceuticals, pesticides, plastics, agriculture, petrochemicals, perfumery, and as electroplating intermediates. Now-a-days SAL and its derivatives continues to attract significant interest in variety of applications: antimicrobial, antifungal formulations, metal complexes, schiff base, and as a crosslinker.

Various traditional methods were employed for synthesis of salicylaldehyde such as Reimer-Tiemann reaction, where the yield of SAL was <40%. Side-chain chlorination of o-cresol and saponification of the subsequent dichloromethyl group to produce SAL. Duff reaction of phenol with paraformaldehyde in the presence of magnesium chloride leads to SAL.

F. Wang, J. Xu, S. Liao, One-step heterogeneously catalytic oxidation of o-cresol by oxygen to salicylaldehyde.

Y. She, W. Wang, G. Li, Oxidation of p o-Crcsols to p o-Hydroxybcnzaldchydcs catalyzed by metalloporphyrins with molecular oxygen.

Moreover, these methods had disadvantages such as use of homogeneous catalyst, great amount of NaOH, and generation of toxic wastes etc.

Only few reports have been published on oxidation of o-cresol and selective synthesis of salicylaldehyde (SAL).

US 1,380,277, discloses the method of producing salicylaldehyde and salicylic acid which comprises oxidizing o-cresol in the vapor phase with an oxygen containing gas in the presence of a metallic oxide (molybdenum oxide) as a catalyst.

In literature entitled One-step heterogeneously catalytic oxidation of o-cresol by oxygen to salicylaldehyde by Feng Wang et al., discloses a use of CuCo/C catalyst and pyridine as additive at 90 °C and 6 atm O2 pressure resulted in 73.8% conversion and 57.3% selectivity to SAL. Oxidation of p/o- cresol to p/o- hydroxybenzaldehyde was reported using metalloporphyrins as a catalyst. Iron porphyrins (T(r-0O¾) PPFeCl) and NaOH used at 70 °C at atmospheric O2 pressure to yield 11.5% SAL and 45.8% conversion of o-cresol. Oxidation of cresol isomers was reported using ozone Ϊ-AI2O3 and S1O2. The highest conversion of 38.9 and 45.7 % was reported for Ϊ-AI2O3 and S1O2 however, the products were other than SAL (by-products like tolyl acetate, di-hydroxytoluene and diethyl maleate). Hence, it has been challenging task to develop an efficient process over the available literature, to achieve high yield and conversion at mild reaction conditions. Accordingly, the present inventors developed a selective process for oxidation of o-cresol with a highest conversion of 99 % and wherein the process utilises a catalyst comprising a transition metals impregnated on OMS-2 to achieve selective aldehyde/acid product over other by products.

OBJECTIVES OF THE INVENTION:

• The primary objective of the present invention aims to provide a process and catalyst for selective oxidation of o-cresol.

• One more objective of the present invention is to provide an effective process for conversion of o-cresol to salicylaldehyde without formation of any by products.

SUMMARY OF THE INVENTION:

The present invention aims to provide a process and catalyst for selective (more than 98%) oxidation of o-cresol.

Accordingly, the process for production of selectively salicylaldehyde by oxidation of o-cresol, comprising steps of treating o-cresol with heterogeneous catalyst in presence methanol and oxygen at pressure between 3 to 5 atm for time between 1 to 2 hr. Wherein reaction temperature is between 60-85°C, more preferably between 70 to 80°C for time between 1 to 2 hr and catalyst concentration is between 0.008 to 0.013 wt.%.

In accordance to one of the embodiments, the catalyst is selected from 5% cobalt doped octahedral molecular sieves support, wherein catalyst is having surface area between 80-140 m 2 /g and pore size between 5 to 20 nm.

BRIEF DESCRIPTION OF THE DRAWING

For a more complete understanding of the present invention, reference is made to the following description taken in conjunction with the accompanying drawing. It is to be understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present invention.

Figure 1 : Illustrates a Raman spectra of catalysts A) OMS-2 and B) 5%Co-OMS-2. Figure 2: Illustrates an Efficacy of various catalyst in oxidation of o-cresol as per example 3 (A).

Figure 3 : Illustrates an Effect of different solvents over oxidation of o-cresol as per example 3 (B).

Figure 4: Illustrates an Effect of catalyst loading over oxidation of o-cresol as per example 3 (F).

Figure 5: Illustrates an Effect of metal loading over oxidation of o-cresol as per example 3 (G).

Figure 6: Illustrates an Effect of O2 pressure over oxidation of o-cresol as per example 3 (H). Figure 7: Illustrates an Effect of temperature over oxidation of o-cresol as per example 3 (I).

Figure 8: Illustrates a Reusability experiments of 5%Co/OMS-2 catalyst for o- cresol oxidation as per example 3 (J).

DETAILED DESCRIPTION OF THE INVENTION:

The present invention developed a selective process for oxidation of o-cresol (Scheme II) over Scheme I and hence provides an industrial feasible process wherein the process utilises a catalyst comprising different transition metal cobalt on support of octahedral molecular sieve (OMS-2). o-cresol salicylaldehyde (SAL)

Reaction scheme II: Selective Oxidation of o-cresol to salicylaldehyde (SAL)

The present invention aims to provide a process and catalyst for selective oxidation of o-cresol. Accordingly, the process for production of selectively salicylaldehyde by oxidation of o-cresol, comprising steps of treating o-cresol with heterogeneous catalyst in presence methanol and molecular oxygen at pressure between 3 to 5 atm for time between 1 to 2 hr. Wherein reaction temperature is between 60-85 °C for time between 1 to 2 hr and catalyst concentration is between 0.008 to 0.013 wt.%.

In accordance to one of the embodiments, the catalyst is selected from 5% cobalt doped octahedral molecular sieves (OMS-2) support. The present invention relates to a development of octahedral molecular sieves (OMS-2) catalyst for catalytic oxidation of o-cresol. Different transition metals from columns III to VIII, specifically V, Cr, Fe, Mo, and Co are doped on said octahedral molecular sieves to check their catalytic activity in presence of various oxygen sources such as air, hydrogen peroxide (H2O2), molecular oxygen (O2), tert- butyl hydrogen peroxide (TBHP).

Wherein, transition metals selected from columns III to VIII, specifically V, Cr, Fe, Mo, and Co is used to give respective M/OMS-2 catalysts and, were tested for their effect on o-cresol oxidation using molecular oxygen.

Accordingly, the selective oxidation of o-cresol was studied for bi-functional M/OMS-2 catalyst. Among all the catalysts 5%Co/OMS-2 nanorods, synthesized by the hydrothermal followed by impregnation method was the best catalyst giving complete conversion of o-cresol, and 98% yield of SAL at 80 °C and 5 atm O2 pressure. The reaction mechanism is that, the selected catalyst 5%Co/OMS-2 has metal sites (S m ) as well as weak basic sites (S t> ), which aid in selective oxidation of o-cresol. The reaction follows the Mars-van Krevelen mechanism, which involves the participation of oxygen from the surface of M/OMS-2 in the reaction creating a vacancy followed by regeneration of surface oxygen, which was supplied through the oxygen source such as air or molecular oxygen. o-Cresol adsorbs on S b while oxygen adsorbs on S m . This is followed by surface reaction, where the surface lattice oxygen of metal (Co) attacks on adjacent side chain methyl carbon to convert it into aldehyde group, leaving behind oxygen-deficient Co ions. This oxygen deficient Co ions (of site S m ) are immediately replaced by oxygen and thus site is regenerated.

In this invention, different transition metals from columns III to VIII, specifically V, Cr, Fe, Mo, and Co were impregnated on OMS-2 to give respective M/OMS-2 catalysts and, were tested for the selective o-cresol oxidation using molecular oxygen. Different types of oxygen sources: Air, molecular oxygen (O2), tert- butyl hydrogen peroxide (TBHP), and hydrogen peroxide (H2O2) were studied for their efficacy in oxidation of o-cresol. The catalyst were characterized by different techniques: CO2-TPD, BET surface area, FTIR, XRD, FESEM, and EDS.

Examples:

Example 1: Preparation of OMS-2: The catalyst OMS-2 was prepared by hydrothermal method. Manganese sulphate (26 mmol) was dissolved in 50 mL of distilled water to form solution A. Potassium permanganate (18.4 mmol) was dissolved in 50 mL of distilled water to form solution B. The solution B was added dropwise to solution A with vigorous stirring. After addition, the mixture was stirred for next 30 min. It was transferred to a Teflon-lined hydrothermal stainless steel reactor and kept at 160 °C for 24 h. The obtained mass was washed several time with distilled water. It was then filtered, dried at 100°C for 12h and calcined at 500°C for 4 h, obtained material labelled OMS-2. Example 2: Preparation of M/OMS-2: The different M/OMS-2 catalyst (M= Cr, Mo, Co, and Fe) were prepared by impregnation method. In general x wt.% of M/OMS-2 (x= 1-10%) was prepared by dissolving metal precursor in distilled water followed by dropwise addition for 3 h. Water was evaporated and the catalyst mass dried at 120 °C for 12 h followed by calcination at 500 °C for 4 h.

Figure 1 Represent a Raman spectra of A) OMS-2 and B) 5%Co/OMS-2

Table 1 Textural properties of catalyst 1 Catalyst BET surface Total Pore Avg. pore area volume diameter (nm)

(m 2 /g) (cm 3 /g)

OMS-2 119 0.87 15.5 5%Co/OMS-2 111 0.70 12.5 Reused 5%Co/OMS-2 109 0.68 12.2

Table 2 Textural properties of catalyst 2 and 3

Catalyst BET surface Total Pore Avg. pore area volume diameter (nm) (m 2 /g) (cm 3 /g)

OMS-2 122-150 0.88-089 10.6-19.5 5%Co/OMS-2 80-140 0.70-072 8.2-19.2 Reused 5%Co/OMS-2 100-130 0.68-0.69 9.3-18.6

Table 3 CO2-TPD of various synthesized catalyst

CO2-TPD Basicity (mmol/gcat)

# Catalyst Weak Moderate/Strong Total

1 . OMS-2 . 0.36 . 0 . 0.36 .

2 5%Co/OMS-2 0.38 0.15 0.53

3 Reused 5%Co/OMS-2 0.37 0.14 0.51 Table 4 EDS of 5%Co/OMS-2 catalyst

Catalyst Atomic weight percentage (%)

Co Mn O K C

5%Co/OMS-2 5.5 28.6 59.9 2.5 3.5

Example 3: Process of Selective oxidation of o-cresol for synthesis of Salicyl Aldehyde:

Reactor is pressurised autoclave, wherein the experiment 0.0046 mol of reactant (o- cresol) and 0.25 g catalyst were added to the reactor, and O2 was purged through reactor. After achieving the desired temperature, it was pressurized with O2.

A. Efficacy of various catalyst: Different catalyst were tested for their activity against o-cresol oxidation.

Reaction Parameter: 0.01 wt.% catalyst loading, O2 pressure 5 atm, speed of agitation 800 rpm, solvent methanol, temperature 80 °C, total volume 30 cm 3 , and reaction time 2 h.

As depicted in figure 2, OMS-2 in presence of O2 resulted in 25% conversion of o- cresol with selectivity of SAL, SAC, and SA as 42%, 27% and 23% respectively. Furthermore, promotion of Fe, Cr, V, Mo and Co resulted in varying selectivity to products.

The conversion of o-cresol was in the order of:

5%Co/OMS-2 > 5%Mo/OMS-2 > 5%Cr/OMS-2 > (5%V/OMS-2) > 5%Fe/OMS- 2 > OMS-2.

It was found that 5%Co/OMS-2 was the best catalyst among all tested catalyst giving 99% conversion and 98% selectivity to SAL.

The selectivity to SAL was in the order of:

5%Co/OMS-2 > 5%Mo/OMS-2 > (5%V/OMS-2) > 5%Fe/OMS-2 > 5%Cr/OMS- 2 > OMS-2. Since 5%Co/OMS-2 was proven to be the best, giving 99.5% conversion and 98% selectivity to SAF.

B. Effect of different solvents: Reaction Parameter: 5% Co/OMS-2 catalyst, 0.01 wt.% catalyst loading, o-cresol 0.0046 mol, O2 pressure 5 atm, speed of agitation 800 rpm, total volume 30 cm 3 , and reaction time 2 h

Various solvents such as methanol, IPA, acetonitrile, dioxane, and dimethylformamide (DMF) were used for the study. Methanol was the best solvent offering 99.5% conversion and 98% selectivity (Figure 3). In the case of dioxane and DMF conversion was not significant, which might be due to the poor solubility of o-cresol. Secondly, instead of SAF, the polymerized product was formed in both (dioxane and DMF). Acetonitrile gave satisfactory conversion of 92%; however, the selectivity of SAF was decreased to 45.6%) and the remaining was SAC (54.4%). Hence further experiments were performed using methanol.

C. Effect of reaction time

The effect of reaction time on the oxidation of o-cresol was investigated (Table 5). As expected, upto 2 h the selectivity to SAF was >99% and thereafter it decreased. After 2 h there was further oxidation of SAF to SAC, which leads to decrease in selectivity of SAF. Therefore, all further experiments were performed for 2 h. Table 5 Effect of reaction time on the oxidation of o-cresol

# Time Conversion Selectivity Selectivity Yield of Yield of (h) of o-cresol of SAF of SAC (%) SAF (%) SAC (%) (%) (%)

1 1 71 100 - 71 -

2 2 >99 98 2 97.8 2

3 3 >99.5 90.5 18 90.5 18

4 4 >99.5 70 30 70 30 Reaction parameters: o-cresol 0.0046 mol, 5%Co/OMS-2 catalyst, 0.01 wt.% catalyst loading, O2 pressure 5 atm, temperature 80 °C, speed of agitation 800 rpm, solvent methanol, and total volume 30 cm 3 .

D. Effect of various oxygen sources When the air was used, there was 100% conversion; however, it was found that only polymerized products were formed. As H2O2 is highly reactive and sensitive to temperature, the reaction was carried out at a slightly lower temperature (60°C), giving only 20% conversion. Similarly, in the presence of TBHP, there was complete conversion of o-cresol with selectivity to SAL, SAC, and SA as 70, 20.5, and 9.5 %, respectively. While molecular oxygen stands out to be a better source of oxidation, it gave complete conversion and selectivity upto 98%. Hence, O2 was chosen in all further studies.

Table 6 Effect of different oxygen sources on the conversion of o-cresol and selectivity to different products

# Oxygen source Conversion Selectivity of products (%) of o-cresol

(%)

. SAL . SAC . SA . Other l a Air Too - - - 100

2 b+ H2O2 (50%w/w) 20 65.5 15 9.5 10 3 b TBHP(50%w/w) 100 72 7.5 - 20.5 4 a O2 >99 98 2

Reaction conditions: 5%Co/OMS-2 catalyst, 0.01 wt.% catalyst loading, 80 °C, o- cresol 0.0046 mol, speed of agitation 800 rpm, total volume 30 cm 3 , solvent methanol, reaction time 2 h a pressure 5 atm; b Mole ratio of o-cresol: H2O2 and o- cresohTBHP was 1:5; + 60 °C; c polymerized products. F. Effect of catalyst loading

Parameter: o-cresol 0.0046 mol, O2 pressure 5 atm, solvent methanol, temperature 80 °C, speed of agitation 800 rpm, total volume 30 cm 3 , and reaction time 2 h. As depicted in figure 4, the effect of available active sites on the conversion of o- cresol was tested by varying the catalyst loading from 0.008 to 0.013 wt.%. There was an increase in conversion of o-cresol with the respective loading of catalyst mass due to the proportional increase in active sites. Beyond 0.01 wt.% catalyst loading, there was no change in the conversion; hence, 0.01wt% was taken as the optimized quantity for further study.

G. Effect of metal loading

Since Co/OMS-2 was the best catalyst for this reaction, different loadings of Co such as 3, 5, 7, and 9 wt. % were studied for the oxidation of o-cresol (Fig. 5). Among all the loadings, 5% loading of Co/OMS-2 catalyst was the best, as any additional increase in metal loading, there was no proportionately increase in the rate of conversion of o-cresol.

There was no significant change in the selectivity of SAL until 7% of Co; however, at 9%, the selectivity of SAL was 85.5% and that of SAC was increased upto 14.5% (Table 7).

Table 7 Selectivity profile at different metal loadings

Co wt. %

3 5 7 9

Selectivity of SAL 98.5 98 90.5 85.5

(%)

Selectivity of SAC 1.5 2 9.5 14.5

(%) Reaction conditions: Catalyst loading 0.01wt.%., o-cresol 0.0046 mol, O2 pressure 5 atm, solvent methanol, temperature 80 °C, speed of agitation 800 rpm, total volume 30 cm 3 , and reaction time 2 h.

H. Effect of O2 pressure

Oxygen pressure was varied between 3 and 11 atm. At 5 atm, there was 98% selectivity to SAL (Fig. 6). Any further increase in pressure does not change the conversion. However, beyond 5 atm (at 7 and 9 atm) there was polymerization of o-cresol leading to the formation of di, tri, and tetramers of o-cresol, which was confirmed by GCMS analysis. Hence, all further reactions were done at 5 atm O2 pressure.

I. Effect of temperature

The reaction was studied to understand the effect of temperature from 70 to 85 °C. With an increase in temperature, the rate of oxidation was found to be increased. There was a complete conversion of o-cresol at 80 °C. However, beyond 85 °C there was a sharp decrease in the selectivity of SAL (Fig. 7). This was due to the formation of a mixture of polymerized products, which are not detected by GCMS analysis. Therefore, 80 °C was selected as optimized temperature for further studies.

J. Reusability experiments

The catalyst was reused by separating it from reaction mass after each use by filtration. It was then washed several times with solvent methanol, dried at 100 °C and, used for the next cycle. The loss during this treatment was recovered by adding fresh catalyst and maintaining the equal weight for every cycle. Even after four cycles, there was hardly any change in the oxidation activity of the catalyst (Figure 8). Thus, the catalyst was found to maintain its fidelity.