Syntheses of isocyanates via amines and carbonyl fluoride

Journal of Fluorine Chemistry 176 (2015) 26–30

Contents lists available at ScienceDirect

Journal of Fluorine Chemistry journal homepage: www.elsevier.com/locate/fluor

Syntheses of isocyanates via amines and carbonyl fluoride Hengdao Quan a,b,*, Ni Zhang a, Xiaomeng Zhou b, Hua Qian b, Akira Sekiya b a b

School of Chemical Engineering & Environment, Beijing Institute of Technology, 5 South Zhongguangcun Street, Haidian District, Beijing, 100081, China National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Higashi, Tsukuba 305-8565, Ibaraki, Japan

A R T I C L E I N F O

A B S T R A C T

Article history: Received 20 March 2015 Received in revised form 7 May 2015 Accepted 14 May 2015 Available online 22 May 2015

Isocyanates are widely used in many different areas, but the most common synthesis route-phosgene route cannot fit the more and more rigorous restriction of safety and environment. Here, a facile synthesis method of isocyanates via amines and carbonyl fluoride is proven feasibly by expanding its applications to the syntheses of nine different isocyanates. And two differences with the phosgene route are proposed. The reaction could occur under milder conditions and afford isocyanates in good yields, especially for the isocyanates containing electron withdrawing groups. It is appealing for industrial application. ß 2015 Elsevier B.V. All rights reserved.

Keywords: Amines Carbonyl fluoride Isocyanates Synthesis

1. Introduction Isocyanates, such as toluene diisocyanate (TDI), hexamethylene diisocyanate (HDI), and methylenediphenyl diisocyanate (MDI), 5Isocyanato-1-(isocyanatomethyl)-1,3,3-trimethylcyclohexane (IPDI), are important commercial raw materials in the synthesis of polyurethanes and are manufactured on a very large scale for a broad range of applications. Currently, the global isocyanate market grows by 5% per year, stimulated primarily by the polyurethane output expansion [1]. Furthermore, isocyanates can be used as precursors in the synthesis of herbicides [2], in gun spray painting, in the formulation of varnish, as a component in thermo-plastic resins, printing ink, foundry moulds [3], and isocyanate-based coatings [4]. Nowadays, phosgenation of both aliphatic and aromatic amines is the most common and versatile method for the synthesis of isocyanates in the commercial processes, but there are some assignable drawbacks. Given (i) phosgene (COCl2) is extremely toxic (TLV–TWA (ACGIN): 0.1 ppm) and difficult to be transported, stored, and handled in bulk quantities, and (ii) that large amounts of corrosive HCl are produced as a side-product, and (iii) that the hard-to-remove hydrolysable chlorines contained in the final products can be detrimental for the further

* Corresponding author at: National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Higashi, Tsukuba 305-8565, Ibaraki, Japan. Tel.: +81 298 614196; fax: +81 298 614401. E-mail address: [email protected] (H. Quan). http://dx.doi.org/10.1016/j.jfluchem.2015.05.007 0022-1139/ß 2015 Elsevier B.V. All rights reserved.

applications [5–8]. Hence, many efforts have been made to develop alternative reagents or processes, such as triphosgene method, b-elimination of haloform method, Curtius rearrangement, Lossen rearrangement, Hoffmann rearrangement, reductive carbonylation of nitro compounds, dehydration of carbamate anions, thermal decomposition of carbamates [2,9]. To the best of our knowledge, except the production of IPDI and HDI through the thermal decomposition of the corresponding carbamates which are prepared by a phosgene-free urea-based technology [10], all the other routes are still laboratory procedures for several drawbacks. Carbonyl fluoride (COF2) is similar to phosgene in structure and chemical property, and can react with amines at a relatively low temperature. Moreover, the toxicity of COF2 (TLV–TWA (ACGIN): 2 ppm) is about equivalent to one twentieth of phosgene. Besides, our laboratory has developed an efficient synthesis method of COF2 which made a large scale production in industry with low cost possible [11]. Therefore, using the reactions of amines with COF2 to produce isocyanates is attractive industrially. Practically, several literatures referred to the reactions of amines with COF2 have been reported and isocyanates such as (CF3)2CFN5 5C5 5O, SF5N5 5C5 5O, and ArCF2N5 5C5 5O were obtained [12]; but the investigations about this kind of reactions are still quite inadequate. Herein, we synthesized two different types of isocyanates by reacting COF2 with amines. One was isocyanates without electron withdrawing groups, the other was isocyanates containing electron withdrawing groups. The discussion about the differences between the phosgene route and the COF2 route were also conducted.

H. Quan et al. / Journal of Fluorine Chemistry 176 (2015) 26–30

R-NH2

+COF2 ,T1 R-NHCOF −HF

T2 −HF

27

Table 1 The syntheses of the isocyanates without electron withdrawing groups.

R-NCO

Entry

Substrate

COF2 (mmol)

Scheme 1. The main reactions of COF2 with amines. Name

Chemical amount (mmol)

TDA MDA HDA TODA

8 5 9 5

2. Results and discussion 1a 2b 3c 4d

The synthesis process is consisted of two steps. The first step is the reaction between COF2 and the aromatic or aliphatic amines at the room temperature or near. The second step is the decomposition of the intermediate produced in the first step at a higher temperature (Scheme 1, R is the aromatic or aliphatic substituent).

Several widely-used commercial diisocyanates without electron withdrawing groups (Fig. 1.) were synthesized and the results are listed in Table 1. The intermediates and products were identified by nuclear magnetic resonance (NMR). According to Table 1, the two-step process using COF2 instead of phosgene is feasible to produce TDI, MDI, HDI, and TODI. Unlike examples of (CF3)2CFN5 5C5 5O [12a] and SF5N5 5C5 5O [12c], there were no catalysts required. The experimental conditions were mild, which the first steps were carried out at room temperature, and the second steps were conducted at the temperature no higher than 160 8C. However, compare to the phosgene route, the yields of the final products presented here are relatively lower. For example, by reacting TDA, HDA, and MDA with the phosgene, the TDI, HDI, and MDI were obtained by Biskup et al. [13], Perret and Revelant [14], and Lichty and Seeger [15] in >99.5% yield, 97% yield, and 93.7% yield, respectively. Moreover, the main intermediates were found to be formed with the structure of ‘‘FOCHN– R–NHCOF’’, and the compounds that only one amine group reacting with COF2 were not detected. But for phosgene, only one amine group will react with COCl2 at beginning stage and the second one will react with phosgene after the first one is reacted completely, which the main intermediates are in the structure of ‘‘ClOCHN–R–NH2HCl’’ [16,17]. This is very different between COF2 and COCl2.

H2N

Yield (%)

Name

Yield (%)

1 3 5 7

94 66 92 98

TDI 2 MDI 4 HDI 6 TODI 8

93 81 77 74

Isocyanates containing electron withdrawing groups (Fig. 2) were synthesized by COF2 route, and the results are listed in Table 2. The intermediates and products were identified by NMR. Generally, isocyanates containing withdrawing groups, which can be used as medical intermediates, precursors of pesticides, and in some other special fields, are reported relatively difficult to be obtained by the phosgene route or just prepared by other methods. For examples, Pohls et al. [18] reported a process to prepare BSDI based on a reaction of BSDA with phosgene in orthodichlorobenzene solvent at 180 8C, and Heymann et al. [19] used the same substrates but the solvent was changed to be dioxane; Neither of them presented the yield data. TFMPI was reported to be prepared from the reaction of p-aminobenzotrifluoride hydrochloride and phosgene in toluene solvent with a low yield just 42% [20]. Franz and Osuch [21] synthesized pSTI by pyrolysis of p-toluenesulfonyloxamoyl chloride (obtained in 90% yield from the reaction of pSTA with oxalyl chloride) in o-dichlorobenzene solvent with 79% yield. Obviously, from Table 2, using the COF2 method, satisfactory yields of intermediates and final

CH3

CH3

NHCOF

NCO

NHCOF

TDA

1

NCO 2

CH2

CH2

CH2

NH2

MDA

H2N

Name

2.2. Syntheses of isocyanates containing electron withdrawing groups

NH2

NH2

Product

First step: room temperature for 6 h; second step: 160 8C for 30 min, for Entry 1–3. The yields of intermediates and final products were determined by 19F NMR and 1H NMR. a Solvent, chlorobenzene 15 g. b Solvent, dichloromethane 15 g. c Solvent, chlorobenzene 15 g. d Solvent, acetone 15 g, and chlorobenzene 15 g; first step: room temperature for 3 h; second step: reflux temperature, 132 8C.

2.1. Syntheses of isocyanates without electron withdrawing groups

CH3

76 53 53 88

Intermediate

(CH2)6

FOCHN

FOCHN

NH2

NH2 TODA

NCO

(CH2)6

4 NHCOF

OCN

5

HDA

H2N

NHCOF OCN 3

FOCHN

NCO

6

NHCOF 7

(CH2)6

OCN

NCO 8

Fig. 1. Structures of the substrates, the corresponding intermediates, and the isocyanates without electron withdrawing groups.

H. Quan et al. / Journal of Fluorine Chemistry 176 (2015) 26–30

28

H2N

FOCHN

CF3

CF3

TFMPA

FOCHN

NO2

10

NO2

NA

OCN

NO2

11

12

O

O FOCHN

S O

O

S O

pSTA

OCN

13

O H2N

CF3

9

H2N

H2N

OCN

14 O

O

S

NH2

FOCHN

O BSDA

S

NHCOF

OCN

CF3

CF3

FOCHN

CF3 HFPDA

NCO

16

CF3 NH2

S O

O 15

H2N

S O

NHCOF

OCN

NCO CF3 18

CF3 17

Fig. 2. Structures of the substrates, the corresponding intermediates, and the isocyanates containing electron withdrawing groups.

products were obtained in relatively mild conditions without catalysts except intermediate 13. It may be explained that (i) COF2 has higher reactivity towards nucleophiles [22–24], which could compensate the deactivation of –NH2 caused by the electron withdrawing groups, and (ii) the –NH2 is attached to the electron withdrawing group –S(5 5O)2– of pSTA directly, while the others are not, which enhances the deactivation effect. The synthesis processes were continuous; and the solvent reflux was used to prevent the yields decrease may be caused by the possible surface sintering of the intermediates decomposition. Because the decomposition temperature of each carbonyl fluoride intermediate is different, solvents with different reflux temperatures were used, and the boiling point was the key factor in the selection of inert solvents. Furthermore, some intermediates were prone to agglomerate during the reaction, which was not propitious for the technical continuity and the product purity. A solvent with relatively high polarity, such as acetone, was induced with the ability of dissolving the substrates and intermediates

well, avoided the channel blocking and solvent wasting, and showed great performance. Among the two steps of the syntheses of isocyanates, the formation of intermediates is the crucial step. For the formation of intermediate 13, several catalysts were tried, and the results are listed in Table 3. As shown in Table 3 Entry 1, for the strong electron withdrawing effect of sulfonyl, the reaction of p-toluenesulfonamide with COF2 was not proceeded without catalyst. Mayer and Golsch [25] reported a process to prepare arylsulfonyl isocyanates by reacting phosgene with an arylsulfonamide in the presence of a catalytically effective amount of an alkyl isocyanate and/or a protic acid or a salt, which formed an alkylarylsulfonylurea as the intermediate. It is disappointing that the reaction of Entry 2, using the same catalysts described by Mayer and Golsch [25], was not occurred. This may be attributed to that the catalyst of alkyl isocyanate preferred to react with COF2 forming a by-product containing –N(COF)2 group [23] (Scheme 2) rather than to react

Table 2 The syntheses of the isocyanates containing electron withdrawing groups. Entry

1a 2b 3c 4d 5e

Substrate

COF2 (mmol)

Name

Chemical amount (mmol)

TFMPA NA pSTA BSDA HFPDA

5 5 5 5 5

88 88 88–235 88 88

Intermediate

Final product

Name

Yield (%)

Name

Yield (%)

9 11 13 15 17

95 93 Table 3 100 100

TFMPI 10 NPI 12 pSTI 14 BSDI 16 HFPDI 18

88 91 84 97 99

First step: room temperature for 3 h, except Entry 3; second step: heated the intermediate mixtures under reflux temperature with a nitrogen gas stream for 2 h and 3 h for Entry 1–3 and 4–5, respectively. a Solvent, chlorobenzene 30 g; reflux temperature, 132 8C. b Solvent, acetone 15 g, and xylene 15 g; reflux temperature, 140 8C. c Solvent, toluene 30 g; first step: the details are shown in Table 3; second step: reflux temperature, 140 8C. d Solvent, acetone 15 g, and m-dichlorobenzene 15 g; the colorless needle crystal was gained by the recrystalization in toluene; reflux temperature, 171 8C. e Solvent, acetone 15 g, and xylene 15 g; reflux temperature, 140 8C.

H. Quan et al. / Journal of Fluorine Chemistry 176 (2015) 26–30 Table 3 Yields of intermediate 13 using different catalysts. Entry

Catalysts

Reaction condition

Yield %

1 2

– 5 mg Sodium benzenesulfonate + 10 mg 1-Butyl isocyanate 0.05 ml fuming H2SO4 0.05 ml H3PO4 10 wt.% n-C4F9SO3H 0.05 ml CH3COOH 0.05 ml DMAC 0.05 ml DMF

30–100 8C, 8 h 60 8C, 3 h

No reaction No reaction

60 8C, 60 8C, 60 8C, 80 8C, 60 8C, 60 8C,

52 59 70 50 8.2 24

3 4 5 6 7 8

3h 3h 3h 3h 3h 3h

C

O + F

F N

C

N

4.1. Chemicals

O

C

COF F O +COF2

N

Synthetically, the yields of isocyanates without withdrawing groups obtained by COF2 route are generally lower than phosgene route so far, but the gap will be reduced quickly if more studies are conducted; whereas the yields of isocyanates containing electron withdrawing groups are already satisfactory. Besides, the byproduct HF and excess COF2 could be recycled simply. And the COF2 can be introduced into the current isocyanates production units of phosgene route easily, or just with limited modification, owing to the similar structure and physical state to the phosgene. Furthermore, it makes producing different types of isocyanates at low cost by utilizing the same or similar process possible. The twostep COF2 route is very appealing for industry. 4. Experimental

F N

29

C

O + F

Scheme 2. Mechanism of reaction of COF2 with C–N unsaturated bounds.

with arylsulfonamide, so the intermediate alkylaryl sulfonylurea cannot be produced. Several organic and inorganic acids were tried and indicated to be effective. 10 wt.% n-C4F9SO3H, DMAC, and DMF were also effective, the actually catalytic components were deduced to be H2SO3, CH3COOH, and HCOOH, which formed by the decomposition of n-C4F9SO3H, DMAC, and DMF under the reaction conditions. As shown in Scheme 2 [23], the isocyanate reacting with COF2 could generate a compound containing –N(COF)2 group. So, for the COF2 route, in order to avoid this kind of by-product generated, the COF2 must be removed completely before the decomposition process. But for the phosgene route, there is no need to do this. It is another different between COF2 and COCl2. Similar to the phosgene route, large amounts of HF are produced as the main side-product. HF is highly corrosive and very toxic by inhalation [26], but is the principal industrial source of fluorine, and could be used as precursor to many important compounds. So, it is meaningful to recycle the HF whether in security or in economy. In industry process, the recycle of the HF and the remove of the excess COF2 left in the first step could be realized simply by using a rectifying tower connected with the main reactor. The boiling points of the HF (19.5 8C) and COF2 (83.3 8C) are relatively low and quite different, we can transfer the HF and the excess COF2 into the rectifying tower just by controlling the temperature of the main reactor, and the two compounds could be separated by distillation easily. The recovered HF could be used to prepare HCFC-22 (chlorodifluoromethane) [27], and then to produce the main raw material COF2 [11], or to be sold as a commercial product. The recovered COF2 are returned to the raw material batch. 3. Conclusions In this paper, nine different isocyanates, especially the isocyanates containing electron withdrawing groups, were first synthesized by reacting COF2 with amines under relatively milder conditions. Generally, the reactions were no need to be catalyzed except in the synthesis of pSTI. And for the syntheses of isocyanates containing electron withdrawing groups, the solvents were indispensable in the formation and decomposition of the intermediates. Moreover, two main differences between the phosgene route and the COF2 route are reported.

2,4-diaminotoluene (TDA) 99.5+%, toluene-2,4-diisocyanate (TDI) 98.0+%, 4,40 -methylenediphenyl diamine (MDA) 99.5+%, 4,40 -diisocyanato-3,30 -dimethylbiphenyl (TODI) 98.0+%, bis(4-isocyanatophenyl)hexafluoropropane (HFPDI) 98.0+%, 4-aminobenzotrifluoride (TFMPA) 98.0+%, 4-(trifluoromethyl)phenyl isocyanate (TFMPI) 98.0+%, 4-nitrophenyl isocyanate (NPI) 98.0+%, sodium benzenesulfonate 96.0+%, chloroform-d (CDCl3) 99.6 at.%D (0.05 wt.% tetramethylsilane), N, N-dimethylformamide-d7 (DMFd7) 99.5 at.%D, acetone-d6 (CD3COCD3) 99.9 at.%D were purchased from Tokyo Chemical Industry Co., Ltd. (Tokyo, Japan). Dehydrated dichloromethane 99.0+%, chlorobenzene 99.5+%, dimethyl sulfoxide-d6 (DMSO-d6) 99.9+% (0.05 v/v% tetramethylsilane), hexamethylene diamine (HDA) 95.0+%, 3,30 -dimethylbenzidine (TODA) 97.0+%, methylenediphenyl 4,40 -diisocyanate (MDI) 97.0+%, hexamethylene diisocyanate (HDI) 95.0+%, 4,40 -(hexafluoroisopropylidene)dianiline (HFPDA) 97.0+%, p-toluenesulfonamide (pSTA) 98.0+%, p-nitroaniline (NA) 99.0+%, 4,40 -diaminodiphenyl sulfone (BSDA) 95.0+%, p-toluenesulfonyl isocyanate (pSTI) 95.0+%, acetic acid (CH3COOH) 99.5+%, 1-butyl isocyanate 95.0+%, sulfuric acid (H2SO4, fuming 25%), phosphoric acid (H3PO4) 85.0+%, nonafluorobutanesulfonic acid (n-C4F9SO3H) 97.0+%, N,N-dimethyl acetamide (DMAC) 98.0+%, N,N-dimethyl formamide (DMF) 99.5+%, super dehydrated acetone 99.5+%, tetramethyl silane (TMS) 99.9+%, m-dichlorobenzene 98.0+%, super dehydrated toluene 99.5+%, super dehydrated xylene 80.0+% were purchased from Wako Pure Chemical Industries, Ltd. (Osaka Japan). COF2 99.0+% was prepared in our laboratory [11]. N2 (99.999%) was supplied by Taiyo Nippon Sanso Corporation (Japan). CCl3F 99.0+% was purchased from SynQuest Labs, Inc. (USA). 4.2. Instruments and apparatus 1

H NMR and 19F NMR spectra of the substrates, intermediates and products during the syntheses were recorded on a JNM-EX300 (JEOL, 300 MHz) NMR with TMS and CCl3F as internal standards in different solvent, respectively. The inert glove box was used to offer a <1 ppm oxygen and moisture inert atmosphere. The samples of amines, intermediates, isocyanates were prepared in this system. The vacuum line was used to add the COF2 into the reactor precisely. The air in the reactor will be push out by vacuum line and the reactant and dissolve solution have no touch with air and water. 4.3. Synthesis processes The details of synthesis processes and the analytical results are available free of charge via the Internet at Electronic Supplementary information.

30

H. Quan et al. / Journal of Fluorine Chemistry 176 (2015) 26–30

Acknowledgments The authors thank Dr. Guangcheng Yang, Dr. Xiaoqing Jia, Dr. Masanori Tamura, and Dr. Mizukado Junji for their valuable comments and advices.

[10]

Appendix A. Supplementary data [11]

Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.jfluchem.2015.05. 007.

[12]

References [1] E. Delebecq, J.P. Pascault, B. Boutevin, F. Ganachaud, Chem. Rev. 113 (2013) 80–118. [2] A.M. Tafesh, J. Weiguny, Chem. Rev. 96 (1996) 2035–2052. [3] P. Tremblay, J. Lesage, C. Ostiguy, H.V. Tra, Analyst 128 (2003) 142–149. [4] D.A. Wicks, P.E. Yeske, Progr. Organ. Coat. 30 (1997) 265–270. [5] M. Aresta, A. Dibenedetto, E. Quaranta, Green Chem. 1 (1999) 237–242. [6] F. Paul, Coord. Chem. Rev. 203 (2000) 269–323. [7] W.I. Denton, P.D. Hammond, J.A. Wood, Progress for the production of aromatic isocyanates, U.S. Patent 3287387, Nov., 1966. [8] H. Babad, A.G. Zeiler, Chem. Rev. 73 (1973) 75–91. [9] For review different method to synthesize isocyanates, see: (a) YC. Charalambides, S.C. Moratti, Synth. Commun. 37 (2007) 1037–1044; (b) S. Braverman, M. Cherkinsky, L. Kedrova, A. Reiselman, Tetrahedron Lett. 40 (1999) 3235–3238; (c) E.F.V. Scriven, Chem. Rev. 88 (1988) 297–368; (d) H.E. Baumgarten, H.L. Smith, A.J. Staklis, Org. Chem. 40 (1975) 3554–3561; (e) H. Zengel, M. Bergfeld, Preparation of trans-cyclohexane-1,4-diisocyanate, U.S. Patent 4203916, May, 1980. (f) SM. Islam, D. Mal, B.K. Palit, C.R. Saha, J. Mol. Catal. A: Chem. 142 (1999) 169–181; (g) T.E. Waldman, W.D. McGhee, J. Chem. Soc. Chem. Commun. 8 (1994) 957–958; (h) G. Lewandowski, E. Milchert, J. Hazard. Mater. A 119 (2005) 19–24; (i) V.Y. Bordzilovskii, B.M. Sadikov, A.G. Sutulo, J. Appl. Chem. USSR 65 (1992) 145–149; (j) F. Shi, J.J. Peng, Y.Q. Deng, J. Catal. 219 (2003) 372–375; (k) R.G. Deleon, A. Kobayashi, E. Yamauchi, J. Ooishi, T. Baba, M. Sasaki, F. Hiarata, Appl. Catal. A: Gen. 225 (2002) 43–49;

[13]

[14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27]

(l) X.Q. Zhao, Y.J. Wang, S.F. Wang, H.J. Yang, J.Y. Zhang, Ind. Eng. Chem. Res. 41 (2002) 5139–5144; (m) M. Curini, F. Epifano, F. Maltese, O. Rosati, Tetrahedron Lett. 43 (2002) 4895–4897. (a) G. Bohmholdt, J. Disteldorf, P. Kirchner, H.W. Michalczak, Circulation process for the production of aliphatic and cycloali-phatic diisocyanates, U.S. Patent 5087739, Feb., 1992. (b) IHS, Process Economics Program Report 1F: Aliphatic Diisocyanates Processes, Feb 2002 hhttp://www.ihs.com/products/chemical/technology/pep/ aliphatic-diisocyanates-processes.aspxi (accessed Dec. 3, 2014) [Online]. H.D. Quan, M. Tamura, A. Sekiya, Process for production of carbonyl fluoride, W.O. Patent 2007/037468, Apr., 2007. (a) W.M. Beyleveld, B.C. Oxenrider, C. Woolf, Process for preparing fluoroperhaloalkyl isocyanates, U.S. Patent 3795689, Mar., 1974.; (b) B Bernd, H. Hermann, K. Erich, N,N-diaryl carbamoyl fluorides, process for preparing them and their use in the preparation of ureas, and the ureas obtained thereby, EP Patent 0052842 A2, Jun., 1982. (c) JS. Thrasher, J.L. Howell, A.F. Clifford, Inorg. Chem. 21 (1982) 1616–1622; (d) J.W. Thompson, J.L. Howell, A.F. Clifford, Isr. J. Chem. 17 (1978) 129–131. K. Biskup, R. Bruns, W. Lorenz, F. Pohl, F. Steffens, V. Michele, Process for the preparation of isocyanates in the gas phase. U.S. Patent 2010/0152484 A1, Jun., 2010. N. Perret, D. Revelant, Use of a Piston reactor to implement a phosgenation process, U.S. Patent 2011/0306786 A1, Dec., 2011. J.G. Lichty, N.V. Seeger, Method of preparing chemical compounds. U.S. Patent 2362648, Nov., 1944. H.D. Quan, M. Tamura, A. Sekiya, Method for producing isocyanate compound. J.P. Patent 5322183, Oct., 2013. A. Gemassmer, K. Stammheim, Process for the production of 1,4-diisocyanatobenzene, U.S. Patent 2824117, Feb., 1958. P. Pohls, F. Mietmsch, Diarylsulphone derivatives. U.S. Patent 2297024, Sept., 1942. H. Heymann, L.F. Fieser, J. Am. Chem. Soc. 67 (1945) 1979–1986. J.G. Lombardino, C.F. Gerber, J. Med. Chem. 7 (1964) 97–101. J.E. Franz, C. Osuch, J. Org. Chem. 29 (1964) 2592–2595. M. Avataneo, U.D. Patto, M. Galimberti, G. Marchionni, J. Fluorine Chem. 126 (2005) 633–639. F.S. Fawcett, C.W. Tullock, D.D. Coffman, J. Am. Chem. Soc. 84 (1962) 4275–4285. N.R. Patel, R.L. Kirchmeier, Inorg. Chem. 31 (1992) 2537–2540. H. Mayer, D. Golsch, Method for producing arylsulphonic acid isocyanates. U.S. Patent 6949672 B2, Sep., 2005. BOC Industrial Gases, Hydrogen fluoride, anhydrous, in: Safety Data Sheet, BOC Industrial Gases, UK, 2012 (Ver. 1.4). M.J. Christmas, Y.N. Dimitratos, Process for the manufacture of chlorodifluoromethane, W.O. Patent 2006/022763, Mar., 2006.