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The aldol reaction of bio acetone in presence of a strongly basic ion exchange resin was carried out with and without the addition of water in a temperature range between − 30 °C and 45 °C. The conversion, selectivity and service time of the ion exchange resins were investigated in a stirred batch reactor and a continuous fixed bed reactor. For the...
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... was investigated. As described in literature [8][9][10] the reaction of acetone yields DAA, the dehydration from DAA to MO and the consecutive reactions e.g. to isophorone and mesitylene. However, according to our investigations, the GC analysis of the reaction mixture gave hints towards aldol condensation leading to a different reaction scheme (Fig. 2). The primary product of the aldol reaction is DAA. As described in literature, DAA can eliminate water forming MO. Two other products directly based on DAA have been ...
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... possible reaction paths of MO with acetone were identified as illustrated in Fig. 2: in the first case a methyl group can react with the carbonyl carbon of acetone. The resulting product is semiphorone which can also result from the elimination of water out of ...
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... second possibility is the 1,4-Michael addition. Under the given conditions the product of the 1,4-Michael addition will immediately undergo an intramolecular aldol condensation yielding isophorone (Fig. 2). The sequence of Michael addition and intramolecular aldol condensation is also named Robinson annulation ...
Citations
... These types of catalysts exhibit the capacity to facilitate numerous chemical transformations efficiently and have already proven invaluable in water treatment processes such as water softening, complete deionization, and the purification of potable water [4,5]. Nonetheless, it is crucial to acknowledge that these catalysts can experience rapid deactivation due to the elimination or loss of the active sites [6][7][8]. This aspect presents a challenge in maintaining their long-term catalytic efficiency. ...
This study explores the potential of robust, strongly basic type I ion exchange resins—specifically, Amberlyst® A26 OH and Lewatit® K 6465—as catalysts for the aldol condensation of citral and acetone, yielding pseudoionone. Emphasis is placed on their long-term stability and commendable performance in continuous operational settings. The aldol reaction, which traditionally is carried out using aqueous sodium hydroxide as the catalyst, holds the potential for enhanced sustainability and reduced waste production through the use of basic ion exchange resins in heterogeneous catalysis. Density Functional Theory (DFT) calculations are employed to investigate catalyst deactivation mechanisms. The result of these calculations indicates that the active sites of Amberlyst® A26 OH are cleaved more easily than the active sites of Lewatit® K 6465. However, the experimental data show a gradual decline in catalytic activity for both resins. Batch experiments reveal Amberlyst® A26 OH’s active sites diminishing, while Lewatit® K 6465 maintains relative consistency. This points to distinct deactivation processes for each catalyst. The constant count of basic sites in Lewatit® K 6465 during the reaction suggests additional factors due to its unique polymer structure. This intriguing observation also highlights an exceptional temperature stability for Lewatit® K 6465 compared to Amberlyst® A26 OH, effectively surmounting one of the prominent challenges associated with the utilization of ion exchange resins in catalytic applications.
... Hereafter, some insights into these aspects are given. The strong anion exchange resin Amberlyst A26 has several applications, however, most of them are for catalysis [58,59] or the recovery of organic acids [60,61]. As far as the authors are aware, there is yet to be found a study that shows the Amberlyst A26 efficiency towards the recovery of H 2 SO 4 . ...
... To alternatively produce renewable products from isophorone, bio-based acetone is used for the manufacturing of isophorone [1]. The production of bio-based acetone is carried out through fermentation, e.g., the acetone-butanol-ethanol (ABE) fermentation [97][98][99][100]. ...
... The acetone condensation has a complex reaction mechanism with multiple possible reaction products, including mesityl oxide, phorone, mesitylene, isoxylitones, and ketonic resins [5,99,[109][110][111][112]. In 1989, Salvapati et al. described the three-step reaction mechanism of acetone to isophorone shown in Figure 2 as the most likely reaction mechanism for the formation of isophorone [5]. ...
... The reaction starts with acetone (1), which forms diacetone alcohol (4) through aldol reaction [5,99,132,133]. From diacetone alcohol (4), mesityl oxide (3) and iso-mesityl oxide (2) are formed via dehydration [5,99,[134][135][136]. The aldol reaction of diacetone alcohol (4) and acetone yields triacetone dialcohol (9) [5,99,132,137]. ...
Isophorone is a technically important compound used as a high-boiling-point solvent for coatings, adhesives, etc., and it is used as a starting material for various valuable compounds, including isophorone diisocyanate, a precursor for polyurethanes. For over 80 years, isophorone has been synthesized via base-catalyzed self-condensation of acetone. This reaction has a complex reaction mechanism with numerous possible reaction steps including the formation of isophorone, triacetone dialcohol, and ketonic resins. This review provides an overview of the different production processes of isophorone in liquid- and vapor-phase and reviews the literature-reported selectivity toward isophorone achieved using different reaction parameters and catalysts.
In order to develop a 2nd generation polylactic acid (PLA) process, lactide (LD) was synthesized directly from a commercially available 90% aqueous lactic acid (LA) solution. Experiments were conducted in an ordinary continuous flow fixed bed reactor. The reaction was carried out over various zeolites and γ-Al2O3 catalysts. Furthermore, the influence of pressure, temperature and water content in the inlet was studied. The highest LD selectivity of 98.9% was obtained using 90% LA and γ-Al2O3 as catalyst. In addition, it is concluded that LD yield increases when using highly concentrated LA oligomer with a minor amount of water. The catalysts were characterized by inductively coupled plasma atomic emission spectroscopy (ICP-AES), X-ray powder diffraction (XRD), nitrogen adsorption isotherms (BET), temperature programmed desorption of ammonia (NH3-TPD) and pyridine Fourier transformed infrared spectroscopy (Py-FTIR).
