Amine/urea catalysts

Important applications for titanium have been developed in processes involving acetic acid, malic acid, amines, urea, terephthalic acid, vinyl acetate, and ethylene dichloride. Some of these represent large scale use of the material in the form of pipework, heat exchangers, pumps, valves, and vessels of solid, loose lined, or explosion clad construction. In many of these the requirement for titanium is because of corrosion problems arising from the organic chemicals in the process, the use of seawater or polluted cooling waters, or from complex aggressive catalysts in the reaction. [Pg.875]

Berkessel and co-workers synthesized a library of structurally diverse tertiary amine-functionalized catalyst candidates incorporating a chiral 1,2- or 1,4-diamine chiral backbone [231, 232, 246]. Structure-efficiency studies through sequential modification of the diamine backbone, the tertiary amine functionality, the (thio) urea N-substituents as well as of the amide substituent pattern, exemplarily illustrated a Jacobsen-type 1,2-diamine-based structure (figure 6.24), identified... [Pg.231]

Cyclohexanediamine-derived amine thiourea 70, which provided high enantio-selectivities for the Michael addition [77] and aza-Henry reactions [78], showed poor activity in the MBH reaction. This fact is not surprising when one considers that a chiral urea catalyst functions by fundamentally different stereoinduction mechanisms in the MBH reaction, and in the activation of related imine substrates in Mannich or Streclcer reactions [80]. In contrast, the binaph-thylamine thiourea 71 mediated the addition of dihydrocinnamaldehyde 74 to cyclohexenone 75 in high yield (83%) and enantioselectivity (71% ee) (Table 5.6, entry 2) [79]. The more bulky diethyl analogue 72 displayed similar enantioselectivity (73% ee) while affording a lower yield (56%, entry 3). Catalyst 73 showed only low catalytic activity in the MBH reaction (18%, entry 4). [Pg.167]

Amine hydrochloride catalyst for urea formaldehyde resins Properties ... [Pg.129]

An analogous reaction accurs with evolution of nitrogen, when 5-(substi-tuted)amino-1,2,3,4-thiatriazoles react with isocyanate esters at room temperature, preferably in the presence of tertiary amines as catalysts. Addition of a second molecule of isocyanate tends to produce the corresponding ureas (e.g 66).78... [Pg.306]

On the other hand, chiral primary amine-thiourea catalysts 85 and 90 developed by Tsogoeva [125] and Jacobsen [130], respectively, show an opposite sense of relative stereoinduction in the conjugate addition of acyclic ketones to nitroolefins (see Scheme 2.41 for 90). These anti selective catalysts stand in contrast to the usually obtained results which lead to selective formation of the i yn-conflgured diastereoiso-mers. The unexpected situation suggests participation of a Z-enamine intermediate. Moreover, with respect to the electrophile activation by the urea-type catalysts, it is also demonstrated that only one oxygen of the nitro group is bound to the thiourea moiety in an out-of-plane arrangement [125,130]. [Pg.83]

In 2012, the first polymer supported bifunctional primaiy amine-ureas were developed by Portnoy and coworkers. This heterogeneous catalytic system was tested in the Michael addition of acetone, cyclic ketones and aldehydes to aromatic nitro-olefins leading to activities and selectivities unprecedented for immobilised catalysts. Catalyst 41 based on (ll ,2f )-diphenylethylene-1,2-diamine and a L-valine spacer provided the Michael products in yields ranging from 23 to 99% and in high enantioselectivity (up to 99% enantiomeric excess) (Scheme 19.43). Unfortunately, recovery of the polymer-catalyst and reuse was only tested for 3 cycles, maintaining the high levels of enantioselectivity, but with a significant loss in the yield. [Pg.225]

We must mention that intensive research is on-going in the design of metal-free catalysts for the REX ROP of lactide. By comparison with metal-based catalysts like Sn(Oct)2, the advantages of these metal-free catalysts are that they are less harmful for biomedical applications and readily removed during, e.g., extrusion processes. Among the simplest ones, some selected enzymes, tertiary amines, urea- and iodine-based compounds, phosphines and carbenes have proven efficient metal-free catalysts. However, most of these investigations have shown that these metal-free catalysts are less active and may yield intensive side-reactions, such as epimerization, when applied during bulk REX ROP of LA. ... [Pg.107]

Entry amine R catalyst urea yield (%)° oxamide yield (%) =... [Pg.90]

Despite the prevalence of amine/metal or Brpnsted acid/metal binary catalysis, bifunctional (thio)urea/metal binary catalysis finds only limited applications in in cascade or tandem reactions and is much less well developed. This may be due partially to deactivation of the Lewis acidic metal catalysts by coordinative (thio)urea catalysts. The examples reported often adopted the strategy of sequential additions of catalysts and substrates to solve the problans mentioned above. [Pg.411]

The alkylurea 576 and oxamide 577 are formed by oxidative carbonylation of amines under CO pressure using Pd/C as a catalyst[518]. The urea formation proceeds under atmospheric pressure using PdCh and CuCl2[519]. The mono-and double carbonylations of / -aminoethanol (578 and 579) afford the cyclic carbamate (oxazolidinones) 580 and oxamide (morpholinediones) 581 [520,521]. [Pg.106]

Acetoiicetyliition Reactions. The best known and commercially most important reaction of diketene is the aceto acetylation of nucleophiles to give derivatives of acetoacetic acid (Fig. 2) (1,5,6). A wide variety of substances with acidic hydrogens can be acetoacetylated. This includes alcohols, amines, phenols, thiols, carboxyHc acids, amides, ureas, thioureas, urethanes, and sulfonamides. Where more than one functional group is present, ring closure often follows aceto acetylation, giving access to a variety of heterocycHc compounds. These reactions often require catalysts in the form of tertiary amines, acids, and mercury salts. Acetoacetate esters and acetoacetamides are the most important industrial intermediates prepared from diketene. [Pg.478]

The Ford hydroglycolysis process is an example of a combined approach for die depolymerization of PURs. In a reactor, polyurethane foam is reacted with a mixture of water, diethylene glycol, and alkali metal hydroxides at high temperature to form polyols. When sodium hydroxide is added as a catalyst, a cleaner polyol is formed because all of the carbamates and ureas in the product are converted into amines and alcohols by hydrolysis.33... [Pg.544]

Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...