Hexamethyldisiloxane

162.38

162.38

203-492-7

D7M4659BPU

43346

DTXSID4026769

FLUID

29310095

9.23000

4.20

DryPowder; Liquid

0.7638 g/cm³ @ Temp: 20 °C

-66 °C

99.5 °C

33 °F

n 20/D 1.377(lit.)

H2O: 0.00037g/l insoluble

Flammables area

20 hPa (20 °C)

>1 (vs air)

LD50 orally in Rabbit: > 12160 mg/kg LD50 dermal Rat > 2000 mg/kg

0.5-21.8%(V)

1.38e-12 cm3/molecule*sec

Henry's Law constant = 4.53X10-2 atm-cu m/mol at 25 °C

FREEZING POINT: -68 °C|Insoluble in most solvents, water repellent, resistant towards oxidation and chemical attack /Silicone resins/|Hydroxyl radical reaction rate constant = 1.38X10-12 cu cm/molec-sec at 24 °C

Critical temperature: 245 °C

II

3

UN 1993 3/PG 2

3

R11

16-61-62-45-26-53

JM9237000

F,N,T

Stable, but moisture sensitive. Highly flammable. Incompatible with strong acids, strong bases, oxidizing agents.

P210-P273-P391-P403 + P235-P501

H225-H410

SRP: The most favorable course of action is to use an alternative chemical product with less inherent propensity for occupational exposure or environmental contamination. Recycle any unused portion of the material for its approved use or return it to the manufacturer or supplier. Ultimate disposal of the chemical must consider: the material's impact on air quality; potential migration in soil or water; effects on animal, aquatic, and plant life; and conformance with environmental and public health regulations.

European Chemicals Bureau; IUCLID Dataset, Hexamethyldisiloxane (107-46-0) (2000 CD-ROM edition). Available from the database query page: http://ecb.jrc.it/esis/esis.php as of July 31, 2006|After the siloxanes class of chemicals was designated to the Interagency Testing Committee (ITC) Priority Testing List, an industry consortium, the Silicones Environmental, Health and Safety Council of North America (SEHSC), worked in cooperation with the ITC and the U.S. Environmental Protection Agency (EPA) to sponsor a voluntary health and safety program for siloxanes. Abstracts of each research report funded through SEHSC are posted under Siloxane Research Program on the SEHSC website [http://www.sehsc.com/srp-research-reports.asp]. The SEHSC also provides information on obtaining full copies of the reports from the EPA on this website.

|Warning|H319 (100%): Causes serious eye irritation [Warning Serious eye damage/eye irritation]|P264, P280, P305+P351+P338, and P337+P313|Aggregated GHS information provided by 199 companies from 2 notifications to the ECHA C&L Inventory.|Danger|H225 (98.99%): Highly Flammable liquid and vapor [Danger Flammable liquids]|P210, P233, P240, P241, P242, P243, P273, P280, P303+P361+P353, P370+P378, P391, P403+P235, and P501|Aggregated GHS information provided by 3663 companies from 22 notifications to the ECHA C&L Inventory. Each notification may be associated with multiple companies.|H225: Highly Flammable liquid and vapor [Danger Flammable liquids]|P210, P233, P240, P241, P242, P243, P280, P303+P361+P353, P370+P378, P403+P235, and P501

Vapors have a very low toxicity for ... humans ... /It/ irritates conjunctiva but does not attack the cornea.|Hexamethyldisiloxane has been noted to give off vapors which are transiently irritating to the conjunctiva, but no injury has been observed.

Hexamethyldisiloxane was detected in two separate domestic waste sites in Munich Germany at concentrations of 0.01 and 0.31-0.45 mg/cu m(1). Hexamethyldisiloxane was also detected in the respective sewage treatment plants at concentrations of 0.14-0.17 and 0.18-0.20 mg/cu m, respectively(1).

SOURCE DOMINATED: Hexamethyldisiloxane was detected but not quantified in volatile chemical emissions from sponge rubber, bonded urethane and prime urethane carpet cushions(1).

Hexamethyldisiloxane was detected but not quantified in volatile chemical emissions from sponge rubber, bonded urethane and prime urethane carpet cushions(1). Hexamethyldisiloxane was detected but not quantified in emissions from new carpet vapors(2).

... Hexamethyldisiloxane (HMDS) coadministered with ethinyl estradiol (EE) did produce a small, but statistically significant reduction in uterine weight compared to EE alone.

LD50 Rat oral > 5000 mg/ kg|LD50 Mouse ip 4500 mg/kg

Hexamethyldisiloxane's production and use as a chemical intermediate in the synthesis of silicone fluids, elastomers and fluorosilicone oils as well as in photolithography(1), personal care products and cosmetics(2) may result in its release to the environment through various waste streams(SRC).

TERRESTRIAL FATE: Based on a classification scheme(1), an estimated Koc value of 4,600(SRC), determined from a log Kow of 4.2(2) and a regression-derived equation(3), indicates that hexamethyldisiloxane is expected to have slight mobility in soil(SRC). Volatilization of hexamethyldisiloxane from moist soil surfaces is expected to be an important fate process(SRC) given a estimated Henry's Law constant of 0.0453 atm-cu m/mole(4). Hexamethyldisiloxane is expected to volatilize from dry soil surfaces(SRC) based upon a vapor pressure of 42.1 mm Hg(5). However, adsorption to soil is expected to attenuate volatilization(SRC). No biodegradation data regarding hexamethyldisiloxane were found; however, dimethyl siloxanes in general are highly resistant to biodegradation(6). As a member of this class biodegradation is not expected to be an important fate process.|TERRESTRIAL FATE: Poly(dimethylsiloxane) (PDMS) fluids in intimate contact with many soils undergo siloxane redistribution and hydrolysis, resulting in the formation of low molecular weight cyclic and linear oligomers. Low molecular weight hydroxy-functional hydrolysis products are water soluble, and the cyclics and trimethylsiloxy-end-blocked oligomers are volatile, thus providing materials which can partition from the soil to the water and atmospheric environmental compartments(1). /Poly(dimethylsiloxane)/|AQUATIC FATE: Based on a classification scheme(1), an estimated Koc value of 4,600(SRC), determined from a log Kow of 4.2(2) and a regression-derived equation(3), indicates that hexamethyldisiloxane is expected to adsorb to suspended solids and sediment(SRC). Volatilization from water surfaces is expected(3) based upon a Henry's Law constant of 0.0453 atm-cu m/mole(4). Using this Henry's Law constant and an estimation method(3), volatilization half-lives for a model river and model lake are 1.3 hours and 5 days, respectively(SRC). However, volatilization from water surfaces is expected to be attenuated by adsorption to suspended solids and sediment in the water column. The estimated volatilization half-life from a model pond is 30 days if adsorption is considered(5). According to a classification scheme(6), an estimated BCF of 340(SRC), from its log Kow(2) and a regression-derived equation(7), suggests the potential for bioconcentration in aquatic organisms is high(SRC). Polydimethylsiloxane fluids undergo siloxane bond rearrangement to form low molecular weight linear and cyclic oligomers that are water soluble(8), indicating that hydrolysis of hexamethyldisiloxane may be an important environmental fate process leading to products that will predominantly partition into the atmosphere. No biodegradation data regarding hexamethyldisiloxane were found; however dimethyl siloxanes in general are highly resistant to biodegradation(9). As a member of this class biodegradation is not expected to be an important fate process.|ATMOSPHERIC FATE: According to a model of gas/particle partitioning of semivolatile organic compounds in the atmosphere(1), hexamethyldisiloxane, which has a vapor pressure of 42.1 mm Hg at 25 °C(2), is expected to exist solely as a vapor in the ambient atmosphere. Vapor-phase hexamethyldisiloxane is degraded in the atmosphere by reaction with photochemically-produced hydroxyl radicals(SRC); the half-life for this reaction in air is estimated to be 18 days(SRC), calculated from its rate constant of 1.4x10-12 cu cm/molecule-sec at 25 °C(3). Methyl siloxanes are transparent to UV radiation >290 nm(4) and therefore hexamethyldisiloxane is not expected to undergo direct photolytic degradation(SRC).

The rate constant for the vapor-phase reaction of hexamethyldisiloxane with photochemically-produced hydroxyl radicals has been reported as 1.4X10-12 cu cm/molecule-sec at 25 °C(1). This corresponds to an atmospheric half-life of about 18 days at an atmospheric concentration of 5X10+5 hydroxyl radicals per cu cm(1). Polydimethylsiloxane fluids undergo siloxane bond rearrangement to form low molecular weight linear and cyclic oligomers that are water soluble(2), indicating that hydrolysis of hexamethyldisiloxane may be an important environmental fate process leading to products that will predominantly partition into the atmosphere. Methyl siloxanes are transparent to UV radiation >290 nm(3) and therefore hexamethyldisiloxane is not expected to undergo direct photolytic degradation(SRC).

An estimated BCF of 340 was calculated for hexamethyldisiloxane(SRC), using a log Kow of 4.2(1) and a regression-derived equation(2). According to a classification scheme(3), this BCF suggests the potential for bioconcentration in aquatic organisms is high(SRC), provided the compound is not metabolized by the organism(SRC).

The Koc of hexamethyldisiloxane is estimated as 4,600(SRC), using a log Kow of 4.2(1) and a regression-derived equation(2). According to a classification scheme(3), this estimated Koc value suggests that hexamethyldisiloxane is expected to have slight mobility in soil.

The Henry's Law constant for hexamethyldisiloxane is 0.0453 atm-cu m/mole(1). This Henry's Law constant indicates that hexamethyldisiloxane is expected to volatilize rapidly from water surfaces(2). Based on this Henry's Law constant, the volatilization half-life from a model river (1 m deep, flowing 1 m/sec, wind velocity of 3 m/sec)(2) is estimated as 1.3 hours(SRC). The volatilization half-life from a model lake (1 m deep, flowing 0.05 m/sec, wind velocity of 0.5 m/sec)(2) is estimated as 5 days(SRC). However, volatilization from water surfaces is expected to be attenuated by adsorption to suspended solids and sediment in the water column. The estimated volatilization half-life from a model pond is 30 days if adsorption is considered(3). Hexamethyldisiloxane's Henry's Law constant indicates that volatilization from moist soil surfaces may occur(SRC). Hexamethyldisiloxane is expected to volatilize from dry soil surfaces(SRC) based upon a vapor pressure of 42.1 mm Hg(4).

... SILICONES OF A LOW DEGREE OF CONDENSATION CAN PRESENT PROBLEMS IN INDUSTRIALTOXICOLOGY ... HEXAMETHYLSILOXANE /IS A/ ... SUBSTANCE OF RELATIVELY LOW BOILING POINT.|NIOSH (NOES Survey 1981-1983) has statistically estimated that 14,234 workers may be exposed to hexamethyldisiloxane in the US(1). Occupational exposure to hexamethyldisiloxane may occur through inhalation and dermal contact with this compound at workplaces where hexamethyldisiloxane is produced or used(SRC). The most likely pathway by which the general public is exposed to hexamethyldisiloxane is by inhalation and dermal contact when personal care products and cosmetics containing this substance are used(SRC).

To examine the distribution of low molecular weight silicones in body organs, separate groups of female CD-1 mice were injected with either breast implant distillate composed primarily of hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, dodecamethylcyclohexasiloxane, and tetradecamethylcycloheptasiloxane or a polydimethylsiloxane oil containing low molecular weight linear siloxanes. Mice were injected subcutaneously in the suprascapular area and killed at different times. Levels of individual low molecular weight silicones were measured in 10 different organs (brain, heart, kidney, liver, lung, mesenteric lymph nodes, ovaries, spleen, skeletal muscle, and uterus). In mice treated with the cyclosiloxane mixture and killed at 3, 6, or 9 weeks, highest levels of cyclosiloxanes were found in the mesenteric lymph nodes, ovaries, and uterus, but all organs examined contained cyclosiloxanes. In a cohort killed at 1 year, most organs contained measurable cyclosiloxanes with highest levels in mesenteric lymph nodes, abdominal fat, and ovaries. Of the individual cyclosiloxanes measured, selective retention of decamethylcyclopentasiloxane and dodecamethylcyclohexasiloxane relative to octamethylcyclotetrasiloxane was seen in all organs at all time points studied. Organs from animals receiving the linear siloxane mixture were harvested at 9, 12, and 15 weeks. ... Maximum levels in the brain, lungs, and mesenteric lymph nodes /were found/, but all other organs contained measurable levels. These data are, to the best of our knowledge, the first demonstration that after a single subcutaneous injection silicones are widely distributed throughout the body and can persist over an extended period.

Urine is a primary route of elimination of hexamethyldisiloxane (MM) in the form of metabolites. Accordingly, to aid in the pharmacokinetic investigations, major metabolites of MM were identified in urine collected from Fischer rats (F-344) administered (14)C-MM orally and via intravenous injection ... The structural assignments were based on GC-MS analysis of the tetrahydrofuran or methylene chloride extracts of urine containing the metabolites. Some of the metabolites in the extract required protection with trimethylsilyl groups prior to GC-MS analysis using bis(trimethylsilyl)trifluoroacetamide or highly purified hexamethyldisiloxane ... The following are among the major metabolites identified: Me2Si(OH)2; HOMe2SiCH2OH; HOCH2Me2SiOSiMe2CH2OH (predominant); HOCH2Me2SiOSiMe3; HOMe2SiOSiMe3; Me3SiOH. Besides these there were also three other metabolites- HOMe2SiOSiMe2CH2OH, 2,2,5,5- tetramethyl-2,5-disila-1,3-dioxalane and 2,2,5,5-tetramethyl-1,4-dioxa-2,5- disilacyclohexane inferred from GC-MS analyses. Their presence in the HPLC metabolite profile was not established. No parent MM was present in urine. The presence of certain metabolites such as Me2Si(OH)2 and HOMe2SiCH2OH clearly established some demethylation at the silicon-methyl bonds. Metabolites of this linear siloxane are structurally different from that obtained for cyclic siloxanes (D4 and D5) except for the commonly present Me2Si(OH)2. A mechanistic pathway for the formation of the metabolites was proposed.|Major metabolites of hexamethyldisiloxane (MM) a... were identified in urine collected from Fischer (F-344) rats administered (14)C-MM ... orally and via intravenous injection. ... The following are among the major metabolites identified in the case of MM: Me(2)Si(OH)(2), HOMe(2)SiCH(2)OH, HOCH(2)Me(2)SiOSiMe(2)CH(2)OH, HOMe(2)SiOSiMe(2)CH(2)-OH, HOCH(2)Me(2)SiOSiMe(3), and Me(3)SiOH. No parent MM ... was present in urine. The presence of certain metabolites such as HOMe(2)SiCH(2)OH and Me(2)Si(OH)(2) in MM ... clearly established the occurrence of demethylation at the silicon-methyl bonds. Metabolites of the linear siloxane are structurally different from that obtained for cyclic siloxane except for the commonly present Me(2)Si(OH)(2). Mechanistic pathways for the formation of the metabolites were proposed.|Phenyltrimethylsilane given intragastrically to rats was absorbed and eliminated in urine. Three percent of total urinary activity was shown to be from hexamethyldisiloxane.

Basic Treatment: Establish a patent airway (oropharyngeal or nasopharyngeal airway, if needed). Suction if necessary. Encourage patient to take deep breaths. Watch for signs of respiratory insufficiency and assist ventilations if necessary. Administer oxygen by nonrebreather mask at 10 to 15 L/min. Monitor for pulmonary edema and treat if necessary ... . Monitor for shock and treat if necessary ... . Anticipate seizures and treat if necessary ... . For eye contamination, flush eyes immediately with water. Irrigate each eye continuously with 0.9% saline (NS) during transport ... . Do not use emetics. For ingestion, rinse mouth and administer 5 ml/kg up to 200 ml of water for dilution if the patient can swallow, has a strong gag reflex, and does not drool ... . /Irritating materials/|Advanced treatment: Consider orotracheal or nasotracheal intubation for airway control in the patient who is unconscious, has severe pulmonary edema, or is in severe respiratory distress. Early intubation at the first sign of upper airway obstruction may be necessary. Positive-pressure ventilation techniques with a bag valve mask device may be beneficial. Consider drug therapy for pulmonary edema ... . Monitor cardiac rhythm and treat arrhythmias if necessary ... . Start IV administration of D5W /SRP: "To keep open", minimal flow rate/. Use 0.9% saline (NS) or lactated Ringer's if signs of hypovolemia are present. For hypotension with signs of hypovolemia, administer fluid cautiously. Watch for signs of fluid overload ... .Treat seizures with diazepam or lorazepam ... Use proparacaine hydrochloride to assist eye irrigation ... . /Irritating materials/

/HUMAN EXPOSURE STUDIES/ /Hexamethyldisiloxane/ was submitted to determine its ability to sensitize the skin of normal volunteer subjects using a repeated insult patch test. One-hundred subjects completed the study. Patches were applied to the infrascapular area of the back. The entire study extended over a six week period. It involved three phases: induction, rest, and challenge. The induction phases consisted of nine consecutive applications and subsequent evaluations of the test sites. The rest period lasted fourteen days. The challenge phase used identical patches applied to sites previously unexposed to the test material. Under the conditions employed in this study, there was no evidence of sensitization to the test substance.|/SIGNS AND SYMPTOMS/ Hexamethyldisiloxane has been noted to give off vapors which are transiently irritating to the conjunctiva, but no injury has been observed.|/OTHER TOXICITY INFORMATION/ Vapors have a very low toxicity for ... humans. ... /it/ irritates conjunctiva but does not attack the cornea.

hexamethyldisiloxane

All other basic inorganic chemical manufacturing|Disiloxane, 1,1,1,3,3,3-hexamethyl-: ACTIVE|... Used as a hydraulic fluid and comes in contact with heated metal surfaces of engines operating at high temperatures. /Organo Silicate MLO 5277/

Cosmetics -> Antifoaming; Antistatic; Emollient; Skin conditioning