Al-MCM-41: An Efficient and Recyclable Heterogeneous Catalyst for the Synthesis of ββ-Hydroxy Thiocyanates inWater

An efficient and green procedure has been developed for the synthesis of ββ-hydroxy thiocyanate by the regioselective ring opening of epoxides with NH4SCN. e reaction was carried out in water without any organic solvent at 40 C, using Al-MCM-41 (a mesoporous aluminosilicate) as catalyst. In this method, several types of epoxides carrying electron-donating or withdrawing groups were rapidly converted to the corresponding ββ-hydroxy thiocyanates in good from excellent yields. Various advantages associated with this protocol include simple workup procedure, short reaction times, high product yields, greater regioselectivity, and easy recovery and reusability of the catalyst.


Introduction
Chemical processes employ large amounts of hazardous and toxic solvents.One of the challenges for the chemists is to come up with new approaches that are less hazardous to human and environment.e choice of pursuing a low waste route and reusable reaction media and minimizing the economic cost and environmental impact of a chemical process is becoming ever more urgent for the future.One of the most promising approaches uses water as reaction medium.Water is an abundant, cheap, nontoxic, and nondangerous solvent [1].
From green chemistry point of view, there is an increasing demand for transformation of homogeneous into heterogeneous catalysis in organic synthesis, especially in �ne chemical synthesis due to the ease with which catalysts can be separated from products and recycled [6].Microand mesoporous materials offer unique opportunities for heterogeneous catalysis by their large surface area.Recently, a wide range of acid-base or redox catalysts have been developed by modi�cation of such material via introducing active elements inside the pore walls [7,8].Mesoporous aluminosilicate, Al-MCM-41, is well known to show remarkable acidic properties.Since its pore sizes are larger than those of zeolites, bulky organic substrates can contact acid sites of mesoporous aluminosilicates [9].erefore, Al-MCM-41 molecular sieves have been shown to catalyze several organic transformations under vapor or liquid phase reaction conditions [10][11][12].
Because of the importance of -hydroxy thiocyanates in the �eld of synthetic organic chemistry [13] and in continuation of our ongoing effort to introduce novel catalysts for organic transformation [14][15][16][17][18], in this project we decided to explore the use of nanosized Al-MCM-41 as an efficient catalyst for the synthesis of -hydroxy thiocyanates by the regioselective ring opening of epoxides under mild and ecofriendly conditions (Scheme 1).

Result and Discussion
First, the Al-MCM-41 was prepared in our laboratory according to the reported method (Figure 1) [19].
en, the Al-MCM-41-catalyzed ring opening of epoxide was applied to synthesis of various -hydroxy thiocyanates in the presence of thiocyanate anion in water.e reaction was  In the present conversion, epoxide is activated by the acidic proton of Al-MCM-41, which undergoes a nucleophilic attack by SCN − anion (Scheme 2).
In all cases, very clean reactions were observed, and the structures and the regiochemical ratios of products were determined by FT-IR, 1 H NMR, and 13 C NMR spectroscopy and also by comparison with authentic compounds.It is also worth mentioning that the Al-MCM-41 catalyst was easily recovered by simple �ltration, and showed no appreciable loss of activity and without any variation in the reaction times or the yields of the corresponding products when recycled several times (Figure 2).
In conclusion, we have developed a novel, facile and efficient ring opening of epoxides that with SCN − as nucleophiles in the presence of Al-MCM-41.Mild reaction condition, simplicity in operation, low environmental impact and high yields of products can be considered as an advantage of this method.

General Comments.
Products were characterized by comparison of their physical data, IR, 1 H NMR, and 13 C NMR spectra with known samples.NMR spectra were recorded in CDCl 3 on a Bruker Avance DPX 400 MHz spectrometer using TMS as an internal standard.IR spectra were recorded on a BOMEM MB-Series 1998 FT-IR spectrometer.

Synthesis of Al-MCM-41.
Al-MCM-41 were syntheses starting from a mixing solution of NaOH (4.04 g in 120 ml distilled water) and silicic acid (16.08 g) at 75 ∘ C for 1 h and then, it was slowly added to cetyltrimethyl ammonium bromide (9.0 g) under vigorous stirring.Aer 1 hour, this solution was added to an aqueous suspension of aluminum sulfate drop by drop under continuous stirring.e resultant gel was transferred into a te�on-lined stainless steel autoclave under autogenous pressure and treated hydrothermally at 110 ∘ C for 4 days.e solid product was obtained aer cooling to room temperature, �ltering, washing, and drying at 110 ∘ C for 6 hours.Finally, the product was calcined at 500 ∘ C for 5 hours.

Typical Procedure for the Preparation of 𝛽𝛽-Hydroxy
iocyanates Catalyzed by Al-MCM-41.Epoxide (1.0 mmol) was added to a suspension of Al-MCM-41 (100 mg), which was pretreated in vacuo at 120 ∘ C for 1 hour and NH 4 SCN (228 mg, 3.0 mmol) in water (5 mL).e mixture was magnetically stirred at 40 ∘ C for the time shown in Table 1.Aer complete consumption of epoxide as judged by TLC (using nhexane/ethylacetate (5: 1) as eluent), the insoluble Al-MCM-41 catalyst was �ltered off and the �ltrate was extracted with ether (3 × 5).e extract was dried over Na 2 SO 4 and evaporated in vacuo to give the alcohols.e crude products were puri�ed by silica gel column chromatography.