4,4'-Methylenedianiline enables eco-friendly polyurea polymer synthesis

General Description

4,4'-Methylenedianiline is a chemical compound with various physical and chemical properties, including a faint fishlike odor, insolubility in water, and solubility in alcohol, benzene, and ether. It has numerous applications in different industries, such as the production of polyurethane foams, epoxy resins, urethane elastomers, adhesives, and rubber processing chemicals. However, it is also a carcinogen and has restricted use due to potential health risks. Studies on workers exposed to 4,4'-Methylenedianiline indicated a decrease in its levels over time and provided insights into its elimination and accumulation in the body.

Figure 1. 4,4'-Methylenedianiline

Properties

4,4'-Methylenedianiline exhibits various chemical and physical properties. With a molecular weight of 198.26 g/mol, it appears as tan flakes or lumps and has a faint fishlike odor. It is insoluble in water and can be found in the form of dry powder, other solid, pellets, or large crystals. When crystallized from water or benzene, it forms tan flakes, lumps, or pearly leaflets. The compound has a faint, amine-like odor and a boiling point of 398 °C. Its melting point ranges from 91.5 to 92 °C, and it has a flash point of 220 °C. 4,4'-Methylenedianiline is slightly soluble in cold water but very soluble in alcohol, benzene, and ether. It has a density of 1.15 at 77 °F, making it denser than water, and a vapor density of 6.8, indicating that it is heavier than air. The compound oxidizes in air, turning from pale yellow to dark color. When heated to decomposition, it emits highly toxic fumes of aniline and NOx. Additionally, it is classified as a weak base with a logP value of 1.6, indicating its hydrophobic nature. ¹

Applications

4,4'-Methylenedianiline has various applications in different industries. It is primarily used in the production of 4,4-'methylenedianiline diisocyanate and other polymeric isocyanates, which are essential for manufacturing polyurethane foams. 4,4'-Methylenedianiline also acts as a curing agent for epoxy resins and urethane elastomers, making it valuable in adhesive and adhesive remover products, including glues, paints, inks, dental bonding agents, and microelectronic encapsulations. Additionally, 4,4'-Methylenedianiline serves as a corrosion preventative for iron and an antioxidant for lubricating oils. It is utilized as a rubber processing chemical and as an intermediate in the production of elastomeric fibers like Spandex. 4,4'-Methylenedianiline plays a role in the preparation of azo dyes and is involved in the determination of tungsten and sulfates. Furthermore, the isocyanates derived from 4,4'-Methylenedianiline are incorporated into semiflexible polyurethane foams used for automobile safety cushioning. It should be noted that 4,4'-Methylenedianiline is listed as a carcinogen and has restricted use due to its potential health risks. ²

Body burden

4,4'-Methylenedianiline is a chemical compound used in various industrial processes. Body burden refers to the amount of a substance present in an individual's body. Analysis of urine samples collected from workers involved in MDA production showed a decrease in MDA levels over time. In 1970, 14.9% of samples had MDA levels above 200 ppb, while in 1980, only 0.09% of samples had levels above 20 ppb. This indicates a significant reduction in 4,4'-Methylenedianiline exposure. Further studies on workers exposed to 4,4'-diaminodiphenylmethane, which is used as a curing agent containing 4,4'-Methylenedianiline, revealed important information about its elimination and accumulation. Male workers at a specific work site showed an elimination rate of 0 to 90 μmol/hr. The cumulated excretion amount ranged from 0.04 to 1.2 μmol per day on workdays and 0.005 to 0.51 μmol daily on weekends. Blood concentrations of 4,4'-diaminodiphenylmethane in these workers ranged from 10 to 60 nmol/L. Moreover, urine samples collected at the end of work shifts from workers exposed to 4,4'-diaminodiphenylmethane contained average concentrations of 236 μg/g creatinine (August 1988), 98 μg/g creatinine (October 1988), 50 μg/g creatinine (June 1989), 202 μg/g creatinine (May 1990), and 43 μg/g creatinine. These findings provide insights into the body burden and elimination of 4,4'-Methylenedianiline in workers exposed to it. ³

Reference

1. 4,4'-Methylenedianiline. National Center for Biotechnology Information, 2023, PubChem Compound Summary for CID 7577.

2. PubChem Annotation Record for 4,4'-DIAMINODIPHENYLMETHANE. National Center for Biotechnology Information, 2023, Hazardous Substances Data Bank.

3. IARC; IARC Monographs on the Evaluation of the Carcinogenic Risk of Chemicals to Humans. Some Chemicals Used in Plastic and Elastomers. 1986, 39: 347-365.

General Description

4,4'-Methylenedianiline is a versatile compound used as a reactant in the synthesis of aryl carbamates and 4,4'-diphenylmethane diisocyanate, as well as in the trans-ureation process to produce polyurea polymers. It also acts as a catalyst in the N-arylation of α-amino acids, offering a greener route for solid-phase organic synthesis. However, its release into the environment poses hazards, with potential persistence and limited degradation in air, soil, and water. Occupational and general population exposure risks necessitate proper handling and disposal measures. Monitoring and mitigation efforts are vital to minimize environmental contamination and human health risks associated with 4,4'-Methylenedianiline.

Figure 1. 4,4'-Methylenedianiline

Applications in organic synthesis

Reactant

4,4'-Methylenedianiline is a versatile compound that finds applications as a reactant in various processes. One such application involves the carbonylation of 4,4’-Methylenedianiline with di-Ph carbonate (DPC) using an organic acid and a tertiary amine catalyst to prepare aryl carbamates. These carbamates can be further converted into 4,4'-diphenylmethane diisocyanate (MDI) by heating them at temperatures between 200 to 230°C in a nonpolar solvent with an inhibitor like benzoyl chloride. Additionally, 4,4’-Methylenedianiline can be used in the trans-ureation process, where biscarbamates react with amines or mixed amines in polar solvents such as DMSO and tetramethylene sulfone. This reaction occurs without the need for any catalyst and results in the formation of polyurea polymers with high molecular weights. Notably, these green-chemistry processes offer efficient routes for producing isocyanate products, urea prepolymers, urea elastomers, and urea plastics. Importantly, these processes achieve excellent yields without relying on reactive phosgene or separately synthesizing 4,4'-diphenylmethane diisocyanate in the trans-ureation polymerizations. Overall, 4,4’-Methylenedianiline serves as a crucial reactant in these applications, enabling the synthesis of diverse compounds in a more environmentally friendly manner. ¹

Catalyst

4,4'-Methylenedianiline has several applications as a catalyst, including in the N-arylation of α-amino acids with aryl halides. In this process, 4,4’-Methylenedianiline is used as a crosslinker to prepare polyvinyl alcohol-based resins that demonstrate good hydrophilic and swelling properties. The prepared resins are then used for solid-phase organic synthesis (SPOS), where α-amino acids are immobilized on them through esterification reactions. The immobilized α-amino acids undergo a solid-phase N-arylation reaction in the presence of 4,4’-Methylenedianiline as a catalyst and cuprous iodide as a co-catalyst under milder and greener conditions than free resin protocols. The corresponding N-arylated α-amino acids are obtained in high to excellent yields after hydrolysis of the immobilized product. The PVA-based resins were characterized by FTIR and 1H-NMR to determine their properties such as epoxy equivalent weight (EEW) of epoxidized PVA and density. This method offers an efficient and environmentally friendly route for synthesizing N-arylated α-amino acids using 4,4’-Methylenedianiline as a catalyst. ²

Environmental hazards

4,4'-Methylenedianiline is a chemical intermediate used in the production of isocyanates, polyurethane foams, spandex fibers, epoxy resins, and various other products. Its release into the environment through waste streams poses potential environmental hazards. When released into the air, 4,4'-Methylenedianiline exists in both vapor and particulate phases, where it can be degraded by photochemically-produced hydroxyl radicals, with a half-life of approximately 12.8 hours. In soil, 4,4'-Methylenedianiline is expected to have slight to no mobility and limited volatilization, while biodegradation is not a significant fate process. Upon release into water, 4,4'-Methylenedianiline is anticipated to adsorb to suspended solids and sediment, with low bioconcentration in aquatic organisms and minimal biodegradation. The compound's lack of hydrolysis potential further contributes to its environmental persistence. Occupational exposure can occur through inhalation and dermal contact, and the general population may also be exposed via consumer products containing 4,4'-Methylenedianiline. The extensive use of 4,4'-Methylenedianiline across various industries raises concerns about its environmental impact. Due to its limited mobility, potential for adsorption to soil and sediment, and low biodegradability, 4,4'-Methylenedianiline has the potential to persist in the environment, leading to long-term exposure risks for both workers and the general population. Therefore, proper handling and disposal methods are crucial to minimize environmental contamination and human exposure to 4,4'-Methylenedianiline. Efforts to monitor and mitigate its release into the environment are essential to safeguard ecological and human health. ³

Reference

1. Processes for producing aryl carbamates, isocyanates and polyureas using diaryl carbonate. 2013, Patent Number: US20130079542.

2. Introduction of two polyvinyl alcohol resins for efficient solid support Cu-catalyzed N-arylation of α-aminoacids with aryl halides in aqueous media. Journal of Applied Polymer Science, 2019, 136: 23.

3. PubChem Annotation Record for 4,4'-DIAMINODIPHENYLMETHANE。National Center for Biotechnology Information, 2023, Source: Hazardous Substances Data Bank.

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