WO2021233976A1

WO2021233976A1 - Process for the synthesis of isocyanate-free omega-hydroxy-urethanes, alpha-omega-diurethanes and oligo (poly)urethanes

Info

Publication number: WO2021233976A1
Application number: PCT/EP2021/063249
Authority: WO
Inventors: Francesco Nocito; Michele Aresta; Angela Dibenedetto
Original assignee: Consorzio Interuniversitario Nazionale Per La Reattivita' Chimica E La Catalisi; Catalisi Innovativa Per Il Riciclo Del Carbonio E Biopolimeri S.R.L.
Priority date: 2020-05-19
Filing date: 2021-05-19
Publication date: 2021-11-25
Also published as: IT202000011626A1; EP4153649A1

Abstract

The synthesis of omega-hydroxyalkyl-urethanes, and of alfa-omega-diurethanes is reported which includes the reaction of diols with urea in presence of catalysts based on Ce at temperatures between 125 and 170°C over 4-8 h reaction time. A process for the production of oligomers of omega-hydroxyalkyl-urethanes is also reported based on the reaction of urea with diols in presence of Ce or Zr catalysts or Ce mixed oxides at 125-170°C over 4-20 h.

Description

PROCESS FOR THE SYNTHESIS OF ISOCYANATE-FREE OMEGA-HYDROXY-URETHANES, ALPHA-OMEGA-DIURETHANES AND

OLIGO (POLY)URETHANES

This invention relates to the reaction of diols and urea to afford omega- hydroxyalkyl-urethanes, alfa-omega-diurethanes and oligo(omega-hydroxyalkyl- urethanes) under metal catalysis, avoiding the use of isocyanates or phosgene. The diols can be biosourced. The oligomers or polymers are known as NIPUR (Non- IsocyanatePolyUrethanes).

State of the art

Polyurethanes-PUR represent 5% of the world production of polymers [1] They are a class of materials with large application in the fields of: rigid- and soft-foams, flexible-plastics and elastomers[2,3] In general such PURs are produced by reaction of di- and poly-ols with di- and poly-isocyanates in presence of tertiary amines as basic promoters[4] .Di-isocyanates such as MDI [4,4’-methylene-bis(phenyl isocyanate)] or TDI [toluene-di-isocyanate] are now recognized as cancerogens, mutagens and reprotoxic compounds (CMR) subject to special revision by the EU REACH regulations[5]. Moreover, such isocyanates are prepared by reaction of the corresponding amines with phosgene [6] or by carboxyalkylation of the same amines [7]

Alternatively, PUR can be prepared by reaction of amines with organic carbonates [8] affording materials with higher chemical resistance due to the presence of hydroxy- urethane linkages which increase the stability [9] Monomeric alkyl carbamates (RHN-C0₂R’) are esters of the unstable carbamic acid (RHN-CO2H) [10] and find application mainly in three fields: in polymers as functional group of PUR [11], in peptide chemistry or in related amine-protection [12], as fungicides or herbicides [13], or even in cosmetics. Carbamates can be prepared by reacting alcohols and amines with phosgene or one of its derivatives [14a,b], the reaction of primary or secondary amines with alkyl- or aryl- chloroformates in presence of a base for capturing released hydrogen chloride [14a] being the most common synthetic methodology, even if it is not environmentally friendly and sustainable. The di-urethane of alfa-omega-2-phenyl-propanediol is used as anti- depressive (Felbato , Felbamate^R) [15] It is prepared using multistep synthetic routes that may use phosgene derivatives [15a,b] Alternatively it is produced by reaction of alkyl formate with alkyl acetate [15c] followed by further work up.

The phosgene-free synthesis of cyclic carbamates is based on the following methodologies: insertion of CO2 into aziridines [16], carbonylation of amino-alcohols with CO2 [17], reaction of CO2 with acetylenic amines [18], and reaction of CO2 with propargylic amines and alcohols [19] Worthy to note, only the carbonylation of amino- alcohols follows the rules of green chemistry. Urea has been used in particular conditions for the synthesis of cyclic carbonates from terminal diols [20] EP 2873661 reports the synthesis of trimethylene-carbonates from bio-sourced 1,3-propanediol and urea under heterogeneous catalysis.

Description of the invention

We have found that non vicinal diols can be reacted with urea to afford: i. omega- hydroxy urethanes; ii. alfa-omega-diurethanes; iii. omega-hydroxy linear- oligo(poly)urethanes, by using Ce or Zr compounds (oxides or salts) as heterogeneous catalysts. Depending on the reaction conditions and the used catalysts, the process can be even addressed towards the synthesis of cyclic carbonates and cyclic carbamates.

This invention relates to the synthesis of omega-hydroxyalkyl-urethanes based on the reaction of urea with terminal non-vicinal diols in presence of Ce- or Zr-based catalysts at temperatures between 130 and 150°C and for 4-8 h. In principle, urea can react with a R-OH moiety following two reaction pathways leading to the formation of C-0 (Scheme la) or C-N bonds (Scheme lb) under specific metal-catalysis. Scheme 1. Reaction of urea with an alcoholic moiety with: (a) formation of C-0 bond; (b) formation of a C-N bond.

However, under suited reaction conditions it is possible to address the reaction towards the selective elimination of ammonia or water, to produce the variety of reactions and products shown in Scheme 2. The overall reaction pathway is based on the “extraction of protons” from either the -NH2 or -OH functionalities most likely by the “oxide” linked to the metal. The “hierarchical”, catalyst-driven extraction from -NH2 or -OH will then address the reaction selectively towards either of the products shown in Scheme 1. The elimination of ammonia will afford carbamates, the elimination of water will afford substituted urea. Once the carbamate is formed, the reaction can proceed again with elimination of ammonia or water to afford cyclic compounds as shown in Scheme 2.

Scheme 2. Different products afforded by loss of ammonia or water in the reaction of urea with diols.

Catalysts play a key role in addressing the reaction towards one or the other of the cyclic compounds.

Ce- and Zr- based catalyst are preferably oxides and salts of Ce and/or Zr. Among Ce and/or Zr salts, phosphates such as Ce₃(P0₄)₄ or Zr₃(P0₄)₄ (hereinafter ZrP) are preferred. g-ZrP is a particularly preferred zirconium phosphate.

Ce and Zr mixed oxides are also useful, e.g. of formula xCe02.yZr02 (where O.Kx, y<0.9; x+y=l).

Ce-based catalyst such as CeC or Ce3(P04)4 are preferred.

In the process of the invention, the catalyst is preferably used in a w/w ratio 1-10% with respect to urea, preferably 2-6%. Linear C2-C6 diols optionally substituted by phenyl or C5-C6 cyclic diols may be used in the process of the invention. 3- and 4- C diols can be bio-sourced. Examples of diols include (bio)propanediol, (bio)butanediol, 2-phenyl- propanediol.

The molar ratio diohurea is usually 1:1 in the synthesis of omega- hydroxyalkylurethanes. The reaction is carried out in solvent-free conditions (the diol is the solvent) and formed ammonia is removed from the reaction flask either at ambient pressure or under vacuum. Ammonia can be vented or better trapped into an organic or an inorganic acid solution.

Using ZnO as catalyst, ammonia more than water is eliminated in the first step (Scheme lb). Noteworthy, ZnO dissolves in the reaction mixture and is lost as Zn(NH ) (NCO)2. [21]

When a molar ratio urea: 1,3-propanediol 2:1 is used, the diurethane 9 is produced, isolated as a white solid.

HOCH2CH2CH2OH + 2H₂NC(0)NH₂ = H₂NC(0)[CH₂]₃C(0)NH₂ 9 + NH3

Using 2-phenyl- 1,3 -propanediol as a starting material compound 10 is obtained, which is known as felbamate and used as antidepressive.

CH₂CH(Ph)CH₂OH + 2H₂NC(0)NH₂ = H₂NC(0)[CH₂CH(Ph)CH₂]C(0)NH₂ 10 +

2NH3

This is a particularly interesting result because felbamate is synthesized using multistep routes even using phosgene-derivatives [15]

A further object of this invention is the process for the synthesis of oligomers of omega-hydroxy-alkyl-urethanes comprising the reaction of urea with diols catalyzed by cerium or zirconium catalysts at temperatures in the range 125 - 170°C, preferably 130- 155°C, for 4-20 h, with hierarchical elimination of ammonia and water. Ammonia is released from the reaction mixture also at ambient pressure without vacuum.

Such process, leading the formation of oligo(poly)-urethanes without use of isocyanates, is illustrated in Scheme 3. It consists in the synthesis of monomeric omega- hydroxy-alkylcarbamates from urea and diols (through the elimination of ammonia) and their oligomerization (with elimination of water). The hierarchical elimination of ammonia and water is not an easy process to perform, without incurring in other reactions illustrated in Scheme 2 (cyclization of monomeric omega-hydroxyalkyl-carbamates).

Scheme 3: Hierarchical elimination of ammonia and water from urea and diols with formation of oligomeric urethanes.

Oligomers can be used in a variety of applications including the synthesis of PURs. The invention is better illustrated by the following examples.

Materials

1,3-Propanediol 98%, urea 99%, K₂CO₃99%, nano-sized CeCh_, ZnO 99% and MgO 99,9% were purchased from Sigma Aldrich; 1,4-butanediol 99% was a Alfa Aesar product. Ce3(P04)4 was prepared as reported in ref. [22]

Analytical Methods

FTIR spectra were registered with a Shimadzu Prestige 21 instrument by using either the net sample on KBr discs (if liquid) or its dispersion in Nujol or KBr (if solid), as specified. GC analyses for monomeric cyclic carbonates and cyclic carbamates were carried out using an Agilent 6850 instrument equipped with FID and a Zebron ZB-50 capillary column. Linear carbamates were dosed by HPLC using a Jasco instrument equipped with a UV detector, at 254 nm, and a Rezex ROA column at 40°C with CH3CN / H2O 1 : 1 as mobile phase with a 0.6 mL/min flux. A THERMO GC-TCD equipped with a PLEL 1010 PLOT Supelco capillary column was used for NH3 determination. Multinuclear NMR spectra were recorded by means of a Bruker 600 MHz. LC-MS was carried out with a high accuracy Q-TOF Agilent 6530. A Pulverisette 5 was used for HEM.

General procedure

All catalysts were milled by HEM for 15 min and dried for two hours at 403 K under vacuum before use and were handled and stored under dinitrogen.

Description of Figures

Figure 1 shows the FTIR spectrum of compound 7 obtained from PDO and urea: the signals at 1730 cm ¹ and 1695 cm ¹ are attributed to the C=0 stretching of terminal and internal carbamic moieties. The broad bands between 3070 cm ¹ and 3435 cm ¹ are due to the -NH2, -NH and -OH moieties.

Figure 2a shows the ¹H-NMR spectrum of compound 7 originated from 1,3 -PDO and urea with signal attribution. Figure 2b shows that in D2O, the proton signals of -NH, -NH2 and -OH moieties of 7 disappear due to the H-D exchange with the solvent.

Figure 3 shows the ¹³C spectrum of 7. Signals are coherent with a dimeric structure of the carbamate formed upon water elimination between two monomeric carbamates

Figure 4 shows the LC-MS of oligomeric product 8 obtained from 1,3-BDO and urea (Example 4).

Example 1: Synthesis of 3-hydroxypropyl carbamate 1

5.0 g (65.7 mmol) of 1,3-propanediol, 3.9 g (65.7 mmol) of powdered urea and 0.19 g of catalyst (see Table 1) were placed with a magnetic bar in a 100 mL round bottom flask and the reaction was carried out for 4 or 8 h at 135 or 145°C (see Table 1) under stirring allowing formed NH3 to escape the reaction flask at ambient pressure, or collecting it into a fatty organic acid or inorganic acid (H₂SO₄) in water. At the end, the reaction mixture was extracted with 2x7 mL of CH₃CN removing the unreacted urea and the catalyst. The collected liquid phases were analyzed by GC and HPLC and the carbamate 1, the cyclic carbonate 2, the cyclic carbamate 3 and the un-reacted diol were quantified (see Table 1).

Table 1. Reaction conditions and catalysts for 1,3 -propanediol conversion

Pure 3-hydroxypropyl-carbamate was isolated by column chromatography on Si0₂ using hexane:ethyl acetate=l : 11.5 as eluent. Two runs were necessary in order to separate 1 and the diol linked by H-bonds. Pure 1 is a yellowish liquid that solidifies below 20°C (chromatographic yields are reported in Table 1, isolated yields were 2-4 points lower than GC-yields) characterized by FTIR, 'H and GC-MS.

GC-MS: (m/z 101, 57, 44).

IR (neat cm ¹): v (OH) 3404, v (NH) 3263, v (CH) 2958, v (C=0) 1695, d (NH) 1616, d (OH) 1417, v (CN) 1248, v (C-OH) 1086, d (CH) 742;

¾ NMR: (d-DMSO, ppm): 5.4 (-NH₂), 3.9 (aCH₂-), 3.3 (yCH₂-), 1.8 (pCH₂-); 1³C NMR: (d-DMSO, ppm): 159 (C=0), 61 (yCH₂-), 58 (aCH₂-), 29 (pCH₂-).

Example 2: Synthesis of 4-hydroxybutyl-carbamate 4

5.0 g (55.5 mmol) of 1,4-butanediol, 3.3 g (55.5 mmol) of powdered urea and 0.17 g of catalyst were placed with a magnetic bar in a round bottom 100 mL flask and the mixture was reacted under the conditions reported in Table 2. Table 2: Reaction conditions and catalysts for the reaction of 1,4-BDO with urea

¹ comparative example

Formed ammonia was allowed to escape the reaction vessel and was collected in a solution of organic or inorganic acid. The products and unreacted diol were extracted by using CFFCN (2x7 mL). The collected C¾CN fractions were analyzed by GC and HPLC and the products quantified (Table 1, isolated yields were 2-5 points lower than GC-yield). Carbamate 4 was isolated using the same procedure described for 1 in Example 1 and the pure low melting (24°C) product characterized by FTIR, 'H and ¹³C NMR and GC-MS. GC-MS (m/z 115, 102, 88, 74, 57, 44).

IR (neat, cm ¹): v (OH) 3408, v (NH) 3265, v (CH) 2953, v (C=0) 1690, d (NH) 1618, d (OH) 1423, v (CN) 1248, v (C-OH) 1086, d (CH) 742;

¾ NMR: (d-DMSO, ppm): 5.4 (-NH₂), 4.3 (-OH), 4.0 (aCH₂-), 3.4 (6CH₂-), 1.8 (PCH₂-), 1.4 (yCH₂-); 1³C NMR: (d-DMSO, ppm): 158.2 (C=0), 61 (6CH₂-), 58 (aCH₂-), 28.4 (yCH₂-),

24.6 (PCH₂-). Table 3

Comparative example

As reported in Table 3, nano-sized (50 nm) CeC , used in the same conditions as ZnO, affords the same or even better conversion yields and selectivity towards the mono carbamates and is quantitatively recovered after reaction, while ZnO is dissolved in the reaction mixture as Zn(NH₃)₄(NCO)₂ and lost. The use of Ce or Zr-derivatives is a very positive fact as the catalyst is recovered and recycled, while the product is not contaminated with the metal. In a similar manner the following catalysts: Ce3(P04)4; Zr02; Zr₃(P04)4; xCe0₂ yZr0₂ (where 0.1<x,y<0.9; x+y=l) were used at 418 K for 4 h in the reaction of urea and diols and the yield of the relevant omega-hydroxy-carbamates are reported in square brackets next to the catalyst.

Example 3: Synthesis of dimeric urethane from 1,3-propanediol and urea, 7 5.0 g (65.7 mmol) of 1,3-propanediol, 3.9 g (65.7 mmol) of powdered urea, 0.19 g of CeCk (or any other catalyst mentioned above) were reacted for 15 h at 165°C and a low- melting (above 40°C) waxy product was formed that was extracted with 5 mL of diethyl ether in order to extract the unreacted diol and any other soluble monomeric compound. Then the waxy mass was washed with 1 mL of water to extract urea. The low melting solid was heated at 47°C and filtered using a sintered glass filter in order to separate the catalyst that was recovered. The waxy solid was characterized by FTIR, 'H and ¹³C NMR (see Figs. 1-3) and shown to be a urethane 1 dimer.

In a similar way was synthesized the dimer of 4. Example 4: Synthesis of oligomeric urethanes from 1,4-butanediol, 8.

5.0 g (55.5 mmol) of 1,4-butanediol, 3.3 g (55.5 mmol) of powdered urea, 0.17 g of Ce0₂ were reacted under stirring at 165°C for 15 h with formation of a white waxy product, 8. After work-up as reported in Example 5, a white solid melting above 130°C at ambient pressure was isolated that was characterized by FTIR, NMR and LC-MS and shown to be a mixture of trimers and tetramers of the monomeric carbamate.

Example 5: Synthesis of alfa-omega-propyl-dicarbamates, H₂NC(0)0-CH2-CH2-CH2-0C(0)NH₂ 9

5 g (65.7 mmol) of 1,3 -propanediol, 7.9 g (131.4 mmol) of powdered urea and 0.39 g of Ce0₂ were reacted at 135°C for 4 hours under stirring. At the end of the reaction the mixture was treated with 5 mL of diethyl ether to extract unreacted diol and trimethylene carbonate. 7 mL of acetonitrile were added to the white solid residue, to solubilize 9 for its separation from not soluble catalyst and unreacted urea. 9 was isolated (90%) by concentration of the C¾CN solution as a pure white solid characterized by using FTIR and NMR.

FTIR: v(C=0)= 1705 cm ¹. ¾NMR: OCH2 3.93; CCH₂C 1.78; N H₂ 5.38; [i?N=C(-0H)0] 6.4.

¹³C NMR: C= O 157.2; 0-CH₂ 61.1; C-Clh-C 28.2.

Example 6: One pot synthesis of Felbamate,

H2NC(0)0CH₂CH(Ph)CH₂0C(0)NH210

Using the procedure reported in Example 5, 2-phenyl- 1,3 -propanediol was converted into felbamate in one step. 0.300 g of 2-phenyl- 1,3 -propanediol were reacted with

0.230 g of urea (1 :2 molar ratio) for 8 h at 145°C K. At the end the viscous orange solution was cooled to room temperature and extracted with tetrahydrofuran that extracted the products and left behind the excess solid urea. The THF solution was analyzed by analytical HPLC and showed to contain the starting unreacted product (20-30%, based on different tests), the monocarbamate (10-15 %) and the dicarbamate (60-65%). The latter was isolated by preparative HPLC and characterized by FTIR and 'H and ¹³C NMR.

FTIR: v(C=0)= 1734 cm ¹

¾ NMR (CDCh): CH₂-0 4.73; CCHC 2.776; CeHs 0-7.242, m-7.255, p-7.132; NF/₂5.4 ppm.

¹³C NMR (DMSO-de): CH₂-C(H)(Ph)-CH₂ 40.8; CH₂ 69.8; C_Ph,„ 127.7; C_Ph,_m 128.5; C_Ph,p 128.8; C_Ph-C 141.1; C=0 157.2 ppm. Literature

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Claims

1. A process for the synthesis of omega-hydroxyalkyl-urethanes that includes the reaction of diols with urea in presence of catalysts based on Ce or Zr.

2. A process according to Claim 1 wherein the Ce or Zr-based catalysts are oxides, mixed oxides or salts thereof.

3. A process according to Claim 1 or 2 wherein the catalyst is selected from Ce₃(P0₄)₄, ZrCk , Zr3(P04)4 and xCeCk yZrCk where 0.1<x,y<0.9; x+y=l.

4. A process according to Claim 1 or 2 in which the catalyst is CeCk.

5. A process according to any one of claims from 1 to 4 wherein the weight ratio of catalyst to urea is from 1-10 %, preferably from 2 to 6%.

6. A process according to any one of claims from 1 to 5 wherein the reaction is carried out at temperatures in the range 125-170°C and for times in the interval 4-8 h.

7. A process according to any one of claims from 1 to 6 wherein the diol is a linear C2-C6 diol optionally substituted by phenyl or a C5-C6 cyclic diol.

8. A process according to claim 7 wherein the diol is selected from propanediol, butanediol, 2-phenyl-propanediol.

9. A process according to claim 8 for the preparation of felbamate from 2-phenyl- propanediol.

10. A process according to any one of claims from 1 to 9 wherein the stoichiometric ratio urea:diol is 1 for monourethanes and 2 for diurethanes.

11. A process for the preparation of oligomers of omega-hydroxyalkyl-urethanes comprising the reaction of urea with diols in the presence of Ce or Zr oxides or salts at temperatures in the range 125-170°C for times in the interval 4-20 h, without ammonia removal under vacuum.