Preparation method of n-propylbenzene and its application in organic synthesis_Kain Industrial Additive

Background and overview^[1][2]

Alkylbenzene is an important chemical product that can be directly used as a solvent and an intermediate in the synthesis of other important chemical raw materials. n-propyl benzene can be used in textile dyes, printing, acetate fiber solvents and synthetic polypropylene nucleating agent (bis-1,3,2,4-(4′-propylbenzylidene)-1-propylsorbitol) Intermediate, this nucleating agent has the advantages of high nucleation efficiency, high transparency, good biological adaptability and low odor. With the continuous expansion of research and development of fine chemicals, n-propylbenzene will be used more and more widely. Due to the current high price of n-propyl benzene, the use of n-propyl benzene is subject to certain restrictions. If the synthesis cost of n-propylbenzene needs to be significantly reduced, the preparation of propiophenone by catalytic oxidation is a preferred clean synthesis method. The cost of synthesizing n-propylbenzene using stoichiometric synthesis methods is relatively high and there are environmental pollution problems. Alkylation of toluene side chain methyl groups using base catalysis is the future development direction. In addition, the components of aromatic hydrocarbon fractions containing nine carbon atoms produced by catalytic reforming, cracking to produce ethylene and dry gas to produce ethylbenzene in the petrochemical process include cumene, n-propylbenzene, ethyltoluene, and mesene. Toluene, trimylene, o-trimethylbenzene, indene, etc. How to separate n-propylbenzene from these C9 aromatic hydrocarbon fractions is also the future development direction.

Apply^[1]

N-propyl benzene can be used as a solvent for acetate fiber and dyeing in textile printing; it is used to prepare the components of methyl styrene, asphalt and naphtha. Many literature sources mention the above uses, but no actual use has been found so far. There are two main uses for n-propylbenzene: it is used as a transparent nucleating agent for the synthesis of polypropylene and as an intermediate for phenylacetone.

1. Intermediates for the synthesis of transparent nucleating agents for polypropylene

In 2010, Milliken Chemical launched the latest generation of polypropylene transparent agent Millad NX 8000. The transparency it can achieve has increased many business opportunities. Millad NX 8000 makes transparent polypropylene look similar to polystyrene and polycarbonate. This makes material substitution possible. Transparent polypropylene application areas include: food containers (high-end customers pursue higher transparency); packaging materials (replacing high-cost plastics, such as polycarbonate, polyvinyl chloride, polystyrene and copolyester, etc.); baby bottles ( Replace polycarbonate, based on cost and endocrine gland safety considerations); squeeze-blow plastic bottles (cosmetic containers, etc.). Milliken has applied for a large number of patents regarding the synthesis of Millad NX 8000 polypropylene clarifier. The synthesis route uses n-propylbenzene as raw material to synthesize 4-n-propylbenzaldehyde, and then reacts with sorbitol derivatives. The reaction formula is as follows.

2. Used to synthesize phenylacetone

Phenyl acetone compounds are widely found in natural products and can be used as pharmaceutical active molecules. They are widely used in chemical fields such as medicine and pesticides.

Beijing University of Technology has disclosed a method for bionic catalytic oxygen oxidation of n-propylbenzene to prepare phenylacetone. This method uses n-propylbenzene as raw material, under normal pressure and solvent-free conditions, and uses mononuclear metal porphyrin and μ- Any one or two of the oxygen-binuclear metalloporphyrins are used as catalysts, and oxygen is introduced at a flow rate of 10 ~ 60 mL/min to initiate the reaction at 140 ~ 160℃ , and then react at 70~110℃ for 4~10 h to obtain phenylacetone. In a typical embodiment, 10×10-6 tetrakis-(p-chlorophenyl)cobalt porphyrin and 1×10-6 tetraphenyliron porphyrin are added, and the reaction mixture is distilled under reduced pressure. The yield of phenylacetone It is 70.4%, the purity is 99.1%, and the n-propyl benzene conversion rate is 79.6%. Mn(Br8TPP)Cl conjugated to imidazole-modified polystyrene can serve as a simulated enzymatic oxidation catalyst.

Polystyrene-bonded imidazole (PSI) is not only a heterogeneous axial base but also a carrier for immobilizing Mn(Br8TPP)Cl. In the presence of this catalyst, alkylaromatics and cycloalkanes are efficiently oxidized to their corresponding alcohols and ketones. Ultrasonic irradiation enhances the catalytic activity of the catalyst in alkane hydroxylation, shortens the reaction time and increases the yield. Taking n-propylbenzene as an example, periodic acid is used as the oxidant. Under the action of ultrasound, the conversion rate of n-propylbenzene and the selectivity of phenylacetone can reach 94%. This heterogeneous catalyst has high stability in oxidation reactions.flexibility and reusability. Similarly, PSI immobilized tetraphenylporphyrin manganese(III) chloride can also effectively catalyze the oxidation of alkylarenes and cycloalkanes to produce the corresponding alcohols and ketones.

Preparation of polymerized meso-tetrakis-(4,4′-biphenylene-disulfonyl)-phenylporphyrin and its complexes (PMTBPBSOPP, M=Co , Mn, Cu or Zn) can be used as a catalyst for alkylbenzene side chain oxidation. The structure of polymeric porphyrin and its complexes shows a two-dimensional structure similar to a film. When molecular oxygen is used as the oxygen source, cobalt complexes and manganese The complex has good catalytic activity. When chloramine-T is used as an oxidant together with pure oxygen or air oxygen, metalloporphyrins can catalytically oxidize n-propylbenzene to phenylacetone at room temperature. The catalytic activity of porphyrin complexes strongly depends on the central metal and ligands, among which Fe and Mn complexes show better catalytic activity than the corresponding Co, Ni or Ru complexes. Using molecular oxygen as the oxidant, fluorinated metal porphyrin (TPFPPM, M=Co, Mn or Fe)/high-valent metal salt can catalyze the side chain oxidation of alkylbenzene. For example, adding a trace amount of K2Cr2O7 can significantly promote the oxidation of fluorinated metal porphyrin. The catalytic performance of oxidized ethylbenzene and its derivatives, the conversion rate of ethylbenzene reached 55.2%, and the yield of phenylacetone was 51.0%. The catalytic system also shows good catalytic performance for the oxidation of alkylbenzenes such as n-propylbenzene, n-butylbenzene and 4-ethylbromobenzene.

Preparation^[1-2]

When propylene, 1-chloropropane or n-propanol are used as raw materials for Friedel-Grafts alkylation reaction with aromatics, all the products obtained are isopropyl aromatics. The reason is that an acid catalyst is used and the active species of the reaction is Carbocation, because primary carbocation is unstable, can easily rearrange to form secondary carbocation. Therefore, new reaction pathways must be sought to synthesize n-propylbenzene.

So far, n-propylbenzene has not achieved large-scale commercial production. Public literature reports on the synthesis of n-propylbenzene include the following technical routes:

1) Reaction of benzyl magnesium chloride and diethyl sulfate;

2) Friedel-Grafts acylation reaction with propionyl chloride and benzene and then reduction;

3) Use NaK catalyst to catalyze the reaction of toluene and ethylene to prepare n-propylbenzene, of which 1) and 2) are stoichiometric synthesis methods, and 3) is a catalytic synthesis method.

1. Stoichiometric synthesis method

At present, the method used to synthesize n-propylbenzene is still the classic stoichiometric method, which is the reaction of benzyl magnesium chloride and diethyl sulfate. The reaction formula is as follows.

This method has many shortcomings: 1) Diethyl sulfate is a highly toxic substance, which poses huge safety hazards during production, storage and transportation; 2) The reaction generates a large amount of toxic and harmful waste; 3) Benzyl magnesium chloride is expensive , anaerobic and anhydrous operating conditions are required during the reaction process.

2. Catalytic synthesis method

Catalyze the reaction between toluene and ethylene

The reaction of ethylene and alkylbenzene is carried out in the presence of an alkaline catalyst at 150~200℃ and under certain pressure conditions. The reaction involves substituting ethyl for benzyl hydrogen, such as toluene. n-propylbenzene can be obtained as raw material. Toluene and ethylene are used as raw materials, and NaK alloy is used as a catalyst to catalyze the synthesis of n-propylbenzene. The reaction formula is as follows.

This method requires the water content of the raw material toluene to be 100~350 mg/L and adding tall oil as a dispersant. The catalyst activation temperature and time are 200°C and 2.5 respectively. h, the mixture was cooled to 137~139°C, and then ethylene was introduced. The reaction time was 2.5 h, the reaction pressure was 2.07 MPa, and a flat blade impeller was used to generate strong stirring with high shear force. Under the above conditions, when 1 134 kg of toluene, 59 kg of NaK, and 2 495 kg of ethylene were fed, the chromatographic analysis data of the product were toluene 35.4%, n-propylbenzene 51.0%, 3-phenylpentane 12.3%, indene 0.09% full.