Synthesis And Tanning Properties Of Sulfonated Tetra-(p-Hydroxyphenyl) Calix[4]Resorcine

Calixarenes are known as the third generation supramolecular poster after crown ethers and cyclodextrins. There are many phenolic hydroxyls and hydrophobic cavity on the calixarene molecule. Moreve, calixarenes are mainly used in ionophore and molecular ion recognition. Calixarenes show poor solubility in water, which largely limited the applications. In order to enlarge the application of calixarene, the hydrophilic modification of calixarene has attracted much attention in research, for example, hydrophilic groups such as sulfonic group, carboxyl, amino are introduced in calixarene to get the water-soluble calixarene. For now, sulfonated calixarene is the most widely studied calixarene in the water-soluble calixarene.Chrome tanning is the primary tanning method in tannery due to its excellent leather property. The absorption of tanning agents is very low and about 30-40 percent of chrome tanning agent remains in wastewater. It not only pollutes the environment but also wastes the resource. Whereas, the sulfonated calixarene not only has the good solubility in water but also can connect with the amino of collagen fibers forming hydrogen bond and covalent bond. Besides, the sulfonic group of calixarene up-rim has coordination ability with chrome. In this study, the sulfonated tetra-(p-hydroxyphenyl)calix[4]resorcine was synthesized and applied in chrome-free and less-chrome tanning process as leather tanning agent to reduce chromium amount and pollution.The tetra-(p-hydroxyphenyl)calix[4]resorcine was synthesized by the acid catalytic cycliccondensation which the resorcinol and p-hydroxybenzaldehyde were used as the raw materials. The synthetic process was optimized by adjusting the ratio of reactants, dosage of concentrated hydrochloric acid, ratio of solvent, reaction temperature and reaction time as the factors index of the production yield. The structure and thermal stability of tetra-(p-hydroxyphenyl) calix[4]resorcine was characterized by Fourier Transform InfraredSpectroscopy(FT-IR), Nuclear Magnetic Resonance(NMR), X-ray Single Crystal Diffractometer and Thermogravimetric Analysis(TG).1H NMR results showed that the chemical shift of 5.428ppm was the H atoms of newly generated methine bridge which indicating the tetra-(p-hydroxyphenyl)calix[4]resorcine was successfully prepared. X-ray single crystal diffractometer results indicated that the molecular structure belonged to chair configuration. TG results showed that it cracked at the 320℃ and it had good thermal stability.Water-soluble sulfonated tetra-(p-hydroxyphenyl)calix[4]resorcine was synthesized, which introduced sulfonic group by sulfonation based on the tetra-(p-hydroxyphenyl)calix[4]resorcine. The synthetic process was optimized with the water solubility as index by varying reaction temperature and time. The structure of sulfonated tetra-(p-hydroxyphenyl)calix[4]resorcine was characterized by FT-IR and NMR. FT-IR results indicated that the absorption peak of 1026cm-1 was the stretching vibration absorption peak of S=O.’H NMR results indicated that the H atoms of hydroxyl ortho-position in hydroxy benzaldehyde had no peak and the sulfonic group was introduced successfully in tetra-(p-hydroxyphenyl)calix[4]resorcine.The sulfonated tetra-(p-hydroxyphenyl)calix[4]resorcine was applied in chrome-free and less-chrome tanning of goat picked skin. The tanning process conditions were optimized with the index of shinkage by series of single factor experiments, such as the tanning pH, tanning agent amount and tanning temperature. The application results showed that the sulfonated tetra-(p-hydroxyphenyl)calix[4]resorcine had tanning performance. The shrinkage temperature was 70.9℃ and thickness increment ratio reached 42.2% of the leather tanned by 10% sulfonated tetra-(p-hydroxyphenyl) calix[4]resorcine. Compared to traditional chrome tanning, the physical and mechanical properties of the leather tanned by sulfonated tetra-(p-hydroxyphenyl) calix[4]resorcine was approximate the same quality. The shrinkage temperature of the leather tanned by 6% sulfonated tetra-(p-hydroxyphenyl)calix[4]resorcine combined with 2.5% chromate was 95.8 ℃ and thickness increment ratio reached 50.6%. The chromium content was reduced to 256mg/L. Compared to traditional chrome tanning, the physical and mechanical properties of the leather tanned by 6% sulfonated tetra-(p-hydroxyphenyl)calix[4]resorcine combined with 2.5% chromate was better than traditional chrome tanning. This tanned method effectively reduced the amount of chromate and environmental pollution.