The limiting value of ZDMC formation: new insight into the reaction of ZNO and TMTD

Abstract

The reaction of ZnO and tetramethylthiuram disulfide (TMTD) was reinvestigated in detail. Under conditions where evaporation of volatiles is possible, TMTD and an excess of ZnO are found to produce bis(dimethyldithiocarbamato)zinc(II) (ZDMC) in limiting amounts close to 60 mol %, irrespective of the ratio between ZnO and TMTD. This result points to the operation of more than one route toward ZDMC. When ZnO and TMTD are reacted in closed vessels in inert atmosphere, a nucleophilic reaction of ZnO with TMTD was confirmed by GC-mass spectroscopy (MS) detection of COS and NMR observation of tetramethylthiourea (TMTU). This route is found to account for about 70 mol % of the total amount of ZDMC formed. A previously unrecognized redox reaction between ZnO, sulfur, and TMTD, furnishing ZnSO 4 and ZDMC, is responsible for approximately 15 mol % of the amount of ZDMC. Other products that were detected are CO 2 , CS 2 , and tetramethylurea, whereas ZnSO 3 , ZnS, and dioxygen were absent. Based on the latter observation, the operation of a mechanism constituting radical reduction of water by TMTD, yielding dioxygen, was excluded.

Nanocomposite Formation in Hydrogenated Nitrile Rubber (HNBR)/Organo‐Montmorillonite as a Function of the Intercalant Type

“…The reason for the difference between MMT-ODA and MMT-ODTMA can be attributed to the different reactivities of the primary and the quaternary amines upon curing. [27] They are involved in the generation of vulcanization intermediates [28,29] in which the clay intercalant and the curatives participate. [21] In the case of MMT-ODTMA, we expected to find a regular intercalated organoclay structure.…”

Design of SBS-Modified Bitumen Stabilizer Powder Based on the Vulcanization Mechanism

“…(1) Vulcanization accelerators [26]: Vulcanization accelerators are additives that can accelerate vulcanization reactions, cut down the vulcanizing time, reduce the vulcanizing temperature, reduce the amount of vulcanizer and improve the physical or mechanical properties of the vulcanized rubber, such as tetramethylthiuram disulfide. (2) Vulcanization activator: The vulcanization activator can increase the activity of accelerators, improve the vulcanizing speed and vulcanizing efficiency and improve the properties of vulcanized rubber [27][28][29], such as zinc oxide.…”

N,N?-Pentamethylenethiuram disulfide- andN,N?-pentamethylenethiuram hexasulfide-accelerated sulfur vulcanization. II. Relative stability ofN,N?-pentamethylenethiuram disulfide and tetramethylthiuram disulfide with respect to amine formation

“…The presence of ZnO in CPTD and CPTP6 mixtures suppressed the formation of CPTU, and DSC studies showed no CPTU even at 195°C and no degradation of N,NЈ-dipentamethylenethiuram polysulfides (CPTP), leading to CPTU, was found in isothermal studies at 140°C over a 25-min period. 9 A comparison of TMTU formation in the absence and presence of ZnO was made by heating 8 TMTD was also found to decompose quantitatively into TMTU under the same conditions. Zinc bis(pentamethylenedithiocarbamate) (ZPD) may be added to compounds as an accelerator or it may form in situ during vulcanization, where it results from the interaction of pentamethylenedithiocarbamic acid (Hpmtc) with ZnO, as will be discussed in a later article in this series.…”

“…7 In the presence of ZnO, thiourea does not form, even at 200°C, [3][4][5] although on heating TMTD/ZnO for 16 h at 140°C, TMTU was reported. 8 In a previous article in this series, 9 it was shown that N,NЈ-dipentamethylenethiuram disulfide (CPTD) and N,NЈ-dipentamethylenethiuram hexasulfide (CPTP6) are much less stable than is TMTD and that complete decomposition to N,NЈ-dipentamethylenethiourea (CPTU) and CS 2 occurs at vulcanization temperatures (140°C). ZnO prevents degradation.…”