4,6-diaminoresorcinol dihydrochloride

Structural formula
General
Surname	4,6-diaminoresorcinol dihydrochloride
other names	4,6-diamino-1,3-dihydroxybenzene dihydrochloride 4,6-diaminoresorcinol dihydrochloride (DAR) 4,6-diamino-1,4-benzenediol dihydrochloride (DABDO)
Molecular formula	C 6 H 10 Cl 2 N 2 O 2
Brief description	white to gray powder
External identifiers / databases
CAS number 16523-31-2 EC number 605-395-9 ECHA InfoCard 100.107.852 PubChem 458821 ChemSpider 2015425 Wikidata Q72463084
properties
Molar mass	213.06 g mol −1
Physical state	firmly
Melting point	254 ° C with decomposition
solubility	soluble in water
safety instructions
GHS labeling of hazardous substances Caution H and P phrases H: 315-319-341 P: 501-201-264-280-308 + 313-337 + 313
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

4,6-Diaminoresorcinol dihydrochloride DAR is a symmetrical dihydroxybenzene and phenylenediamine , which is usually present as the more oxidation -stable dihydrochloride salt. With terephthalic acid or terephthalic acid can be 4,6-diaminoresorcinol dihydrochloride for high-performance plastic , poly (p-phenylene-2,6-benzobisoxazole) PBO polymerized are. Intensive research work on high-performance plastics in the 1970s and 1980s also pushed the search for easily available, inexpensive and safely and sustainably accessible monomers such as DAR.

Occurrence and representation

As starting material for 4,6-diaminoresorcinol dihydrochloride, first served resorcinol diacetate (1,3-diacetoxybenzene), which in the first synthesis step, the nitration addition to the desired 4,6-dinitroresorcinol the explosive 2,4,6-Trinitroresorcinol ( styphnic supplies), the must be completely removed from the target product by repeated recrystallization.

Because of the dangerous by-product styphnic acid and the time-consuming cleaning in the first stage, the u. a. as a herbicide used 1,2,3-trichlorobenzene as a favorable starting material identified in which the 2 position is occupied by a chlorine atom and therefore can not be nitrided.

Disadvantages of this synthesis route are the relatively high dilution because of the low solubility of the components in the reaction media , the hydrogenation in Hastelloy reactors and, in particular, the poor availability of the starting compound 1,2,3-trichlorobenzene as a PBT substance . As - albeit questionable - alternative raw material was therefore z. B. the poisonous and strongly allergenic 2,4-dinitrochlorobenzene and the introduction of the meta-permanent oxygen functions with the likewise questionable cumene hydroperoxide are proposed.

As a result of the increasingly problematic availability and high costs of suitable raw materials, syntheses u. a. with resorcinol, which is cheaper nowadays, as a raw material base, which also avoids halides, nitro groups and sulphonic acid groups in the intermediate stages and thus unnecessary salt loads. For example, a patent describes the acetylation of resorcinol with acetic anhydride to 1,3-diacetoxybenzene (step A ), which is converted into 4,6-diacetylresorcinol in a Fries rearrangement (step B ) and then reacted with hydroxylamine hydrochloride to form dioxime (step C ) .

By Beckmann rearrangement arises from the dioxime the corresponding diamide (step D ), the end product 4,6-diaminoresorcinol dihydrochloride with hydrochloric acid (step E ) is hydrolyzed. Steps A and B , as well as D and E can also be carried out as one-pot reactions without isolating the respective intermediate. The total yield is approx. 55% and should favor this synthesis route in view of the inexpensive starting materials and simple process management. Acylation and Fries shift of steps A and B can be avoided while avoiding Friedel-Crafts acylation catalysts , such as. B. AlCl ₃ , ZnCl ₂ or FeCl ₃ , and acetic anhydride with acetic acid / methanesulfonic acid and phosphorus pentoxide as a water-binding medium with yields of up to 90% as a "green" reaction.

properties

4,6-Diaminoresorcinol dihydrochloride is obtained in the synthesis as a white to brown, water-soluble and oxidation-sensitive powder. From hot, dilute hydrochloric acid , it can be recrystallized into white needles with the addition of activated carbon and the reducing agent tin (II) chloride as an oxidation inhibitor, which should be stored under nitrogen . The base, 4,6-diaminoresorcinol, on which the salt is based, is very sensitive to oxidation and changes color quickly in air, but can be stabilized over several weeks by adding 2,000 ppm of SnCl ₂ .

Applications

By condensation of 4,6-diaminoresorcinol dihydrochloride with orthoesters , such as. B. trimethyl orthoacetate ( R = R '= CH ₃ ), low molecular weight linearly condensed benzobisoxazole ring systems are accessible, which have been investigated for their suitability as organic semiconductors .

The main use of 4,6-diaminoresorcinol dihydrochloride is as a monomer in the polycondensation with terephthalic acid or terephthalic acid dichloride in polyphosphoric acid to form poly (p-phenylene-2,6-benzobisoxazole) PBO.

At room temperature, PBO forms lyotropic nematic liquid crystal phases in chlorosulfonic acid or methanesulfonic acid . Films and filaments with exceptional temperature resistance and tensile strength can be extruded from such anisotropic solutions ( dope ) .

Silylation of DAR with the protective group reagent tert -butyldimethylsilyl chloride TBS-Cl and reaction with terephthalic acid dichloride yields a silylated prepolymer, which, in contrast to PBO, can be used in aprotic dipolar solvents such as. B. NMP , DMAc or DMSO is soluble and can be poured from solution to transparent films. When heated to 500 ° C, they turn into PBO films, which only decompose under nitrogen at temperatures> 670 ° C.

The polymer PBO was developed at SRI in Menlo Park and brought to an industrial scale by Dow Chemical . PBO is now being marketed as Zylon® fibers by the Japanese chemical company Toyobo .

Individual evidence

1. ↑ ^{a b c d} Entry on 4,6-Diaminoresorcinol dihydrochloride at TCI Europe, accessed on June 2, 2020.
2. ↑ ^{a b} data sheet 4,6-diaminoresorcinol dihydrochloride from Sigma-Aldrich , accessed on June 2, 2020 ( PDF ).
3. ^ JF Wolfe, BH Loo, FE Arnold: Rigid-rod polymers. 2. Synthesis and thermal properties of para-aromatic polymers with 2,6-benzobisthiazole units in the main chain . In: Macromolecules . tape 14 , no. 4 , 1981, p. 915-920 , doi : 10.1021 / ma5000a005 .
4. ↑ ^{a b} Patent US4766244 : High purity process for the preparation of 4,6-diamino-1,3-benzenediol. Applied October 30, 1986 , published August 23, 1988 , applicant: The Dow Chemical Company, inventor: Z. Lysenko. ‌
5. ↑ RG Pews, Z. Lysenko, PC Vosejpka: A safe cost-efficient synthesis of 4,6-diaminoresorcinol . In: J. Org. Chem. Band 62 , no. 23 , 1997, pp. 8255-8256 , doi : 10.1021 / jo961675g .
6. ↑ Patent US5892116 : Process for producing 4,6-diaminoresorcinols. Filed October 8, 1997 , published April 6, 1999 , Applicants: Daiwa Kasei Industry Co., Ltd., Inventors: J. Kawachi, H. Matsubara, Y. Nakahara, Y. Watanabe. ‌
7. ^ F. Chen, Y. Gao, Y. Xu: Metal free Friedel-Crafts di-acetylation of resorcinol in acetic acid . In: Asian J. Chem. Volume 29 , no. 4 , 2017, p. 749-754 , doi : 10.14233 / ajchem.2017.20224 .
8. ↑ JF Mike, AJ Makowski, M. Jeffries-EL: An efficient synthesis of 2,6-disubstituted benzobisoxazoles: New building blocks for organic semiconductors . In: Org. Lett. tape 10 , no. 21 , 2008, p. 4915-4918 , doi : 10.1021 / ol802011y .
9. ↑ Raj B. Durairaj: resorcinol: Chemistry, Technology, Applications . Springer, Berlin 2005, ISBN 978-3-540-25142-2 , pp. 395-408 .
10. ↑ T. Fukumaru, T. Fujigaya, N. Nakashima: Extremely High Thermal Resistive Poly (p-phenylene benzobisoxazole) with Desired Shape and Form from a Newly Synthesized Soluble Precursor . In: Macromolecules . tape 45 , no. 10 , 2012, p. 4247-4253 , doi : 10.1021 / ma3006526 .