In 1991, Menger and others from Emory University in the United States synthesized a bis-alkane chain surfactant with a rigid spacer group connecting the ionic head group, and named it "Gemini surfactant", that is, Gemini surfactant. [1]. The special structure of Gemini surfactant determines that it has better performance than traditional surfactants. It has two hydrophilic groups and hydrophobic groups, and the two parts are connected through a linking group. The linking group acts as a chemical bond, reducing the electrostatic repulsion between the two polarities and the force between the hydration layers, making the Gemini surface active The agent has low CMC properties. Compared with ordinary surfactants composed of a single alkane chain and a single ionic head group, gemini surfactants have the following characteristic properties [2]: (1) Easily adsorbed on the gas/liquid surface, effectively reducing the surface tension of water; ( 2) It is easy to aggregate to form micelles and has a lower critical micelle concentration; 3) It has a very low Kraff point (4) The combination with ordinary surfactants can produce greater synergistic effects; (5) It has good Excellent calcium soap dispersion properties; (6) Excellent wetting properties. At present, Gemini surfactants have been favored by scientists from all over the world and set off a new research boom. This article reviews the current synthesis methods of various types of Gemini surfactants, briefly introduces the application status of Gemini surfactants in the leather industry, and discusses the current development trends of Gemini surfactants.
2 Synthesis of Gemini Surfactants my country’s research on Gemini surfactants started relatively late, so there is still a certain gap in product development, performance research and application compared with foreign countries. The synthesis research of Gemini surfactant series compounds with novel structures has received more attention.
2.1 Anionic Gemini Surfactants Since 1988, the Okahara research group [3] of Osaka University in Japan has synthesized a series of anionic Gemini surfactants. Diglycidyl ether produced by the reaction of epichlorohydrin and diol (or diphenol) serves as the linking chain. Afterwards, it is reacted with bromoacetic acid, chlorosulfonic acid, propane or phosphoric acid as needed to obtain sulfate ester salt, sulfonate salt, carboxylate salt and phosphate type Gemini surfactant respectively. There are many types of gemini anionic surfactants, mainly including sulfate ester salt, sulfonate ester, carboxylate ester, and phosphate ester type.
2.1.1 Sulfate ester salt type (-OSO3M) and sulfonate type (-SO3M) sulfate ester salt surfactants mainly include higher fatty alcohol sulfate ester salts and higher fatty alcohol ether sulfate ester salts , In addition, there are sulfated oils, sulfated fatty acids, sulfated fatty acid esters, etc. Sulfate salt type surfactant has good foaming ability and washing performance, stable performance in hard water, and the aqueous solution is neutral or slightly alkaline. The synthesis method is to first use phase transfer catalysis to synthesize diepoxy compounds, and then use long-chain fatty alcohols to react with diepoxy compounds to form oligomeric glycols. Finally, under certain conditions, oligomeric glycols are reacted with chlorosulfonic acid or chlorosulfonic acid. Propylene lactone reacts to form sulfate ester salt or sulfonate type gemini surfactant, but its yield is not high [4]. In order to overcome the shortcomings of yield and product purity, Yao Zhigang et al. [5] adopted another synthetic route, using sodium taurine to react with dibromoethane to obtain sodium ethylenediamine diethyl sulfonate, and then reacting with oleoyl chloride to obtain N, N'-sodium bisoleoylethylenediamine diethyl sulfonate greatly improves the yield and purity. Jia Weihong et al. [6] prepared four kinds of rosin-based sulfonate gemini surfactant N, N′-diethyl using dehydroabietylamine, α, ω-dibromoalkane and sodium 2-bromoethyl sulfonate as raw materials. Sodium sulfonate-N,N′-didehydroabidyl-α,ω-diamine. Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy were used to characterize the structures of a series of target products. It was concluded that these four surfactants have good wetting properties and low CMC. Their surface activity varies with the molecular structure. It is enhanced by increasing the length of the connected methylene chain. Sulfate ester salt type and sulfonate type Gemini surfactants are currently the more common anionic Gemini surfactants and are more suitable for industrial large-scale production. However, the disadvantage of this process is that it is time-consuming and uses a large amount of sulfur-containing compounds during the synthesis process. , will cause certain harm to the environment. Therefore, the synthesis process conditions of the above two Gemini surfactants need to be further optimized.
2.1.2 Carboxylate type (-COOM) The earliest synthesized carboxylate surfactant was to use ethylenediamine, octyl chloride and chloroacetic acid as raw materials to synthesize carboxylate Gemini surface Active agent, through this basic reaction, changes the length of the carbon chain and the length of the linking group, and a series of compounds can be synthesized. They have high metal chelating properties, resistance to hard water and good calcium soap dispersing ability [7]. Reports on the synthesis of carboxylate Gemini surfactants are currently rare in China. Du Yiyi et al. [8] synthesized a carboxylate gemini surfactant containing p-phenoxy linking chains and studied the micellization properties. The results showed that the carboxylate gemini surfactant has a very low CMC value. and surface tension. As a new type of detergent additive, it will have great development and application potential.
2.1.3 There are two main methods for synthesizing phosphate type (-OPO3M) phosphate gemini surfactant: one is to react diol with POCl3 in the presence of triethylamine and tetrahydrofuran, Fatty alcohol is added dropwise under stirring, then hydrolyzed and dechlorinated, and finally treated with NaOEt/EtOH; the other is to phosphorylate long-chain alcohols to generate phosphate monoesters, which are then reacted with quaternary ammonium bases to obtain phosphate ester quaternary ammonium salts. Then the linking group is introduced and acidified. In recent years, research on using phosphoric acid or polyphosphoric acid as phosphorylating agent to synthesize phosphate esters has attracted people's attention. Compared with the classic process of using phosphorus oxychloride, phosphorus trichloride or phosphorus pentoxide as the acylating agent, this method has high raw material stability, low toxicity and a relatively simple process. Zheng Guo [9] studied the optimal synthesis process of Gemini phosphate surfactant: P2O5 and n-decyl oligomeric glycol were used as raw materials to synthesize Gemini phosphate surfactant. This surfactant has excellent foam stabilization, It has high emulsifying performance, simple synthesis process and mild reaction conditions. Among them, the optimization of process conditions such as reaction temperature, feed ratio n (n-decyl glycidyl ether:ethylene glycol), catalyst selection and other factors are key issues in the synthesis of phosphate Gemini surfactants, which still need to be further studied. .
2.2 Cationic gemini surfactants. In 1991, Menger and Littan [10] synthesized three kinds of gemini surfactants with rigid linking groups. One of them is a cationic type, using dibromo substituted for alkanes and long surfactants. It is prepared by the reaction of carbon chain dimethyl tertiary amine, and the linking group is benzene ring. The currently synthesized gemini cationic surfactants are mainly biquaternary ammonium salt surfactants, which have good biodegradability and low toxicity. There are two main methods for synthesizing cationic diquaternary ammonium salt surfactants [11]: one is to use dibromo-substituted alkanes and single long-chain alkyl dimethyl tertiary amines (the alkyl group is a linear alkyl group) in anhydrous The quaternization reaction is carried out by heating and refluxing in ethanol; the other method is to heat and reflux 1-bromo long-chain alkane and N, N, N', N'-tetramethylalkyl diamine in absolute ethanol to carry out the quaternization reaction. Quaternization reaction. The first method is suitable when dibromoalkanes are very reactive and readily available. However, due to the expensive price of dibromoalkanes, the second method is often chosen to synthesize bisquaternary ammonium salt surfactants [12]. Brominated long-chain alkanes and N, N, N', N'-tetramethylalkyl diamine are used as solvents in absolute ethanol, heated and refluxed for 2 to 3 days, distilled under reduced pressure to remove the solvent, and recrystallized for purification to obtain product. For example, Chen Fengsheng et al. [13] reacted N, N-dimethylpropanediamine with dodecanoic acid, myristanoic acid, hexadecanoic acid and stearic acid respectively to obtain amido tertiary amine, and then made into hydrochloride, hydrochloric acid The corresponding amide group-containing geminionic surfactant was synthesized from salt and epichlorohydrin in water solvent. The structure was characterized by infrared spectroscopy, mass spectrometry, elemental analysis, and nuclear magnetic resonance spectroscopy, and the surface chemical properties were measured. The amide-containing gemini cationic surfactant has strong surface adsorption and micelle generation capabilities. At present, there are not many research reports on cationic gemini surfactants. The reason is that the theoretical research on the synthesis mechanism, synthesis methods and process conditions are not very mature yet and need to be further studied.
2.3 Non-ionic gemini surfactants There are not many domestic studies on the synthesis of non-ionic gemini surfactants, and most of them only refer to foreign research results [14].
Huang Dan et al. [15] used laureth polyoxyethylene ether (3), maleic anhydride and fumaric acid as main raw materials to synthesize laureth polyoxyethylene ether (3) carboxylate symmetric succinic acid. Diester Gemini surfactant. The cleaning rate was measured to be 99.96. As a washing and bleaching auxiliary, the research and development of Gemini nonionic surfactant has important theoretical significance and application value. 2.4 Zwitterionic gemini surfactants There are few reports on zwitterionic gemini surfactants. Renouf et al. [16] designed and synthesized for the first time two gemini surfactants with zwitterionic end groups, which have stronger surface activity than gemini surfactants with the same head groups. Wang Xiaoke et al. [17] used dodecyl tertiary amine, epichlorohydrin and chloroacetic acid as raw materials to synthesize a new amphoteric gemini surfactant of bisquaternary ammonium carboxymethyl sodium salt using a two-step method, using elemental analysis and infrared spectroscopy. Its structure was characterized, and the effect of reaction conditions on the yield of the synthesis reaction was investigated. It was found that the product yield is better than that of quaternary ammonium salt cationic gemini surfactants and traditional amphoteric surfactants.
3 Application of Gemini surfactant in tanning
3.1 High-efficiency emulsifier, solubilizer and degreasing agent Gemini surfactant has high surface activity and serves as an emulsifier High emulsification efficiency. When the dosage is reduced, the effect can be achieved or even exceed the conventional dosage of single-chain surfactants. The extremely low CMC value allows Gemini surfactant to form micelles at very low concentrations to achieve a solubilizing effect. Therefore, Gemini surfactants can be used as efficient solubilizers, degreasing agents and emulsifiers. A small amount of Gemini surfactant can emulsify, disperse and remove the grease and dirt in raw hides [18].
3.2 Pre-tanning and re-tanning fillers In the leather tanning process, due to the special structure and properties of Gemini surfactant, it has the characteristics of being able to quickly combine with the binding points on the leather collagen to prevent tanning agents The surface is over-tanned due to fast combination with leather fibers; in addition, Gemini surfactant can significantly reduce the surface energy of the solution and accelerate the penetration of tanning agents to achieve rapid tanning, uniform tanning or increase the binding amount to make the finished leather Full of purpose. Gemini surfactant is a linking group that connects two or more monomer surfactants together through chemical bonds to expand its chain structure and increase its molecular weight. It also combines with collagen or tanning agents at multiple points, so that it can also be used as a Retanning fillers. Fatliquor is the most commonly used leather chemical product in the tanning process, and sulfonate leather fatliquor is one of the most important varieties [19]. Zhang Hui et al. [20] prepared a gemini surfactant polymaleic anhydride fatty alcohol monoester sodium salt (PMAMS), and used a softness tester to measure its leather fatliquing performance. The results showed that this gemini surfactant The active agent has good leather fatliquor properties.
3.3 Leveling agent and dyeing auxiliary agent Gemini surfactant has excellent dispersion and high permeability. When used in the leather dyeing process, it can achieve good leveling and dyeing auxiliary effects. The high permeability allows it to quickly combine with leather fibers to achieve a slow dyeing effect. Gemini surfactant has a unique structure with a large number of fiber-philic groups or dye-philic groups. Therefore, Gemini surfactant has good dyeing aid properties.