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{{short description|Aromatic diisocyanate}}

{{Chembox
{{Chembox
| Verifiedfields = changed
| Verifiedfields = changed
| Watchedfields = changed
| Watchedfields = changed
| verifiedrevid = 486591748
| verifiedrevid = 486591748
| Name = 4,4'-Methylene diphenyl diisocyanate
| Name = 4,4′-Methylene diphenyl diisocyanate
| ImageFile = 4,4'-methylene diphenyl diisocyanate.svg
| ImageFile = 4,4'-methylene diphenyl diisocyanate.svg
| ImageFile2 = Methylene-diphenyl-diisocyanate-3D-vdW.png
| ImageFile2 = Methylene-diphenyl-diisocyanate-3D-vdW.png
| ImageName = 4,4'-methylene diphenyl diisocyanate
| ImageName = 4,4'-methylene diphenyl diisocyanate
| PIN = 1,1'-Methylenebis(4-isocyanatobenzene)
| PIN = 1,1′-Methylenebis(4-isocyanatobenzene)
| OtherNames = {{ubl
| OtherNames = {{ubl
| Bis(4-isocyanatophenyl)methane
| Bis(4-isocyanatophenyl)methane
| 1-Isocyanato-4-[(4-isocyanatophenyl)methyl]benzene
| 1-Isocyanato-4-[(4-isocyanatophenyl)methyl]benzene
| 4,4'-Methylene diphenyl diisocyanate
| 4,4′-Methylene diphenyl diisocyanate
| 4,4'-Diphenylmethane diisocyanate
| 4,4′-Diphenylmethane diisocyanate
| [[Bayer]] Desmodur 44
| [[Bayer]] Desmodur 44
| Methylene bis(4-phenyl isocyanate)
| Methylene bis(4-phenyl isocyanate)
Line 18: Line 20:
}}
}}
|Section1={{Chembox Identifiers
|Section1={{Chembox Identifiers
| index1_label = 4,4'-
| ChEBI_Ref = {{ebicite|changed|EBI}}
| ChEBI_Ref = {{ebicite|changed|EBI}}
| ChEBI = 53218
| ChEBI = 53218
Line 23: Line 26:
| CASNo_Ref = {{cascite|correct|CAS}}
| CASNo_Ref = {{cascite|correct|CAS}}
| CASNo = 101-68-8
| CASNo = 101-68-8
| EC_number1 = 202-966-0

| UNII_Ref = {{fdacite|changed|FDA}}
| UNII_Ref = {{fdacite|changed|FDA}}
| UNII = B0LO6BBS8C
| UNII = B0LO6BBS8C
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}}
}}
|Section7={{Chembox Hazards
|Section7={{Chembox Hazards
| GHSPictograms = {{GHS07}}{{GHS08}}
| EUClass = Harmful ('''Xn''')
| GHSSignalWord = Danger
| RPhrases = {{R20}}, {{R36/37/38}}, {{R42/43}}
| HPhrases = {{H-phrases|315|317|319|332|334|335|351|373}}
| SPhrases = {{S1/2}}, {{S23}}, {{S36/37}}, {{S45}}
| PPhrases = {{P-phrases|201|202|260|261|264|271|272|280|281|285|302+352|304+312|304+340|304+341|305+351+338|308+313|312|314|321|332+313|333+313|337+313|342+311|362|363|403+233|405|501}}
| FlashPt = 212–214 °C (Cleveland open cup)
| FlashPt = 212–214 °C (Cleveland open cup)
| PEL = C 0.2 mg/m<sup>3</sup> (0.02 ppm)<ref name=PGCH>{{PGCH|0413}}</ref>
| PEL = C 0.2 mg/m<sup>3</sup> (0.02 ppm)<ref name=PGCH>{{PGCH|0413}}</ref>
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}}
}}


'''Methylene diphenyl diisocyanate''', most often abbreviated as MDI, is an [[aromaticity|aromatic]] di[[isocyanate]]. Three [[isomer]]s are common, varying by the positions of the isocyanate groups around the rings: 2,2'-MDI, 2,4'-MDI, and '''4,4'-MDI'''. The 4,4' isomer is most widely used, and is also known as 4,4'-diphenylmethane diisocyanate.<ref>{{Cite web|url=https://pubchem.ncbi.nlm.nih.gov/compound/4_4_-Diphenylmethane_diisocyanate|title=4,4'-Diphenylmethane diisocyanate {{!}} C15H10N2O2 - PubChem|last=Pubchem|website=pubchem.ncbi.nlm.nih.gov|language=en|access-date=2017-06-25}}</ref> This isomer is also known as '''Pure MDI'''. MDI reacts with [[polyol]]s in the manufacture of [[polyurethane]]. It is the most produced diisocyanate, accounting for 61.3% of the global market in the year 2000.<ref name="Randall">{{cite book |author1=Randall, D. |author2=Lee, S. | title = The Polyurethanes Book | publisher = Wiley | location = New York | year = 2003 | isbn = 978-0-470-85041-1 }}</ref>
'''Methylene diphenyl diisocyanate''' ('''MDI''') is an [[aromaticity|aromatic]] di[[isocyanate]]. Three [[isomer]]s are common, varying by the positions of the isocyanate groups around the rings: 2,2′-MDI, 2,4′-MDI, and '''4,4′-MDI'''. The 4,4′ isomer is most widely used, and is also known as 4,4′-diphenylmethane diisocyanate.<ref>{{Cite web|url=https://pubchem.ncbi.nlm.nih.gov/compound/4_4_-Diphenylmethane_diisocyanate|title=4,4'-Diphenylmethane diisocyanate {{!}} C15H10N2O2 - PubChem|last=Pubchem|website=pubchem.ncbi.nlm.nih.gov|language=en|access-date=2017-06-25}}</ref> This isomer is also known as '''Pure MDI'''. MDI reacts with [[polyol]]s in the manufacture of [[polyurethane]]. It is the most produced diisocyanate, accounting for 61.3% of the global market in the year 2000.<ref name="Randall">{{cite book |author1=Randall, D. |author2=Lee, S. | title = The Polyurethanes Book | publisher = Wiley | location = New York | year = 2003 | isbn = 978-0-470-85041-1 }}</ref>


==Production==
==Production==
Total world production of MDI and polymeric MDI is over 6 million tonnes per year (Mt/a in 2016).
Total world production of MDI and polymeric MDI is over 7.5 million tonnes per year (in 2017).

The largest producer is [[Wanhua|Wanhua Group]] followed closely by [[Covestro|Covestro]].<ref name=icis>{{cite news | last = Gal | first = J. | title = To the Rescue | newspaper = ICIS Chemical Business | date = 2012-02-20 }}</ref> Other major producers are [[BASF]], [[Dow Chemical Company|Dow]], [[Huntsman Corporation|Huntsman]], [[Nippon Polyurethane Industry]], Kumho Mitsui Chemicals. All major producers of MDI are members of the International Isocyanate Institute, whose aim is the promotion of the safe handling of MDI and [[Toluene diisocyanate|TDI]] in the workplace, community and environment.
As of 2019, the largest producer was [[Wanhua Chemical Group]].<ref>{{cite magazine|url=https://cen.acs.org/business/finance/CENs-Global-Top-50-chemical/97/i30|title= C&EN's Global Top 50 chemical companies of 2018 |magazine=Chemical & Engineering News|first= Alexander H.|last=Tullo|date=29 July 2019 |accessdate=15 January 2020|volume=97|issue=30|url-access=limited}}</ref> Other major producers are [[Covestro]],<ref name=icis>{{cite news | last = Gal | first = J. | title = To the Rescue | newspaper = ICIS Chemical Business | url = http://www.icis.com/Articles/2012/02/20/9533156/wanhua-to-the-rescue-of-borsodchem.html | date = 2012-02-20 | access-date = 2020-01-15 | archive-url = https://web.archive.org/web/20120326104610/http://www.icis.com/Articles/2012/02/20/9533156/wanhua-to-the-rescue-of-borsodchem.html | archive-date = 2012-03-26 | url-status = dead }}</ref> [[BASF]], [[Dow Chemical Company|Dow]], [[Huntsman Corporation|Huntsman]], [[Tosoh Corporation|Tosoh]], Kumho Mitsui Chemicals. All major producers of MDI are members of the International Isocyanate Institute, whose aim is the promotion of the safe handling of MDI and [[Toluene diisocyanate|TDI]] in the workplace, community and environment.


The first step of the production of MDI is the reaction of [[aniline]] and [[formaldehyde]], using hydrochloric acid as a catalyst to produce a mixture of diamine precursors, as well as their corresponding polyamines:
The first step of the production of MDI is the reaction of [[aniline]] and [[formaldehyde]], using hydrochloric acid as a catalyst to produce [[4,4'-Methylenedianiline]] and other diamine precursors, as well as their corresponding polyamines:


[[File:Synthesis of 4,4'-diaminodiphenylmethane.svg|400px]]
[[File:Synthesis of 4,4'-diaminodiphenylmethane.svg|400px]]


Then, these diamines are treated with [[phosgene]] to form a mixture of isocyanates, the isomer ratio being determined by the isomeric composition of the diamine. Two different reaction mechanisms for this transformation are possible, namely "phosgenations first" and "step-wise phosgenations".<ref>{{Cite journal|last1=Boros|first1=R. Zsanett|last2=Koós|first2=Tamás|last3=Wafaa|first3=Cheikh|last4=Nehéz|first4=Károly|last5=Farkas|first5=László|last6=Viskolcz|first6=Béla|last7=Szőri|first7=Milán|date=2018-08-16|title=A theoretical study on the phosgenation of methylene diphenyl diamine (MDA)|url=http://www.sciencedirect.com/science/article/pii/S0009261418305049|journal=Chemical Physics Letters|language=en|volume=706|pages=568–576|doi=10.1016/j.cplett.2018.06.024|s2cid=102682388 |issn=0009-2614}}</ref>
Then, these diamines are treated with [[phosgene]] to form a mixture of isocyanates, the isomer ratio being determined by the isomeric composition of the diamine.


[[File:Synthesis of methylene diphenyl diisocyanate.svg|550px]]
[[File:Synthesis of methylene diphenyl diisocyanate.svg|550px]]


Distillation of the mixture gives a mixture of oligomeric polyisocyanates, known as '''polymeric MDI''', and a mixture of MDI isomers which has a low 2,4' isomer content. Further purification entails [[fractional distillation|fractionation]] of the MDI isomer mixture.<ref>{{ Ullmann | author = Six, C.; Richter, F. | title = Isocyanates, Organic | doi = 10.1002/14356007.a14_611 }}</ref>
Distillation of the mixture gives a mixture of oligomeric polyisocyanates, known as '''polymeric MDI''', and a mixture of MDI isomers which has a low 2,4′ isomer content. Further purification entails [[fractional distillation|fractionation]] of the MDI isomer mixture.<ref>{{ Ullmann | author = Six, C. | author2 = Richter, F. | title = Isocyanates, Organic | doi = 10.1002/14356007.a14_611 }}</ref>


==Reactivity of the isocyanate group==
==Reactivity of the isocyanate group==
The positions of the isocyanate groups influences their reactivity. In 4,4'-MDI, the two isocyanate groups are equivalent but in 2,4'-MDI the two groups display highly differing reactivities. The group at the 4-position is approximately four times more reactive than the group at the 2-position due to steric hindrance.<ref name="Randall" />
The positions of the isocyanate groups influences their reactivity. In 4,4′-MDI, the two isocyanate groups are equivalent but in 2,4′-MDI the two groups display highly differing reactivities. The group at the 4-position is approximately four times more reactive than the group at the 2-position due to steric hindrance.<ref name="Randall" />


[[Image:MDI isomers.PNG|500px|center|MDI isomers and polymer]]
[[Image:MDI isomers.PNG|500px|center|MDI isomers and polymer]]


==Applications==
==Applications==
The major application of 4,4'-MDI is the production of rigid [[polyurethane]].<ref>{{cite web | last = Boustead | first = I. | work = Eco-Profiles of the European Plastics Industry | title = Polyurethane rigid foam | year = 2005 | publisher = PlasticsEurope | location = Brussels | url = http://www.isopa.org/isopa/uploads/Documents/documents/rigid%20foam%20LCI.pdf | format = PDF | deadurl = yes | archiveurl = https://web.archive.org/web/20130925082609/http://www.isopa.org/isopa/uploads/Documents/documents/rigid%20foam%20LCI.pdf | archivedate = 2013-09-25 | df = }}</ref> These rigid polyurethane foams are good thermal [[Thermal insulation|insulators]] and used in nearly all freezers and [[refrigerator]]s worldwide, as well as buildings. Typical polyols used are [[polyethylene adipate]] (a [[polyester]]) and [[poly(tetramethylene ether) glycol]] (a [[polyether]]).
The major application of 4,4′-MDI is the production of rigid [[polyurethane]].<ref>{{cite web | last = Boustead | first = I. | work = Eco-Profiles of the European Plastics Industry | title = Polyurethane rigid foam | year = 2005 | publisher = PlasticsEurope | location = Brussels | url = http://www.isopa.org/isopa/uploads/Documents/documents/rigid%20foam%20LCI.pdf | url-status = dead | archiveurl = https://web.archive.org/web/20130925082609/http://www.isopa.org/isopa/uploads/Documents/documents/rigid%20foam%20LCI.pdf | archivedate = 2013-09-25 }}</ref> These rigid polyurethane foams are good thermal [[Thermal insulation|insulators]] and used in nearly all freezers and [[refrigerator]]s worldwide, as well as buildings. Typical polyols used are [[polyethylene adipate]] (a [[polyester]]) and [[poly(tetramethylene ether) glycol]] (a [[polyether]]).


4,4'-MDI is also used as an industrial strength adhesive, which is available to end consumers as various high-strength bottled glue preparations.<ref>{{US patent reference | number = 6884904 | y=2005 | m=04 | d=26 | inventor = Smith, A. K.; Goddard, R. J.; Paulsen, E. J. L. | title = MDI-based polyurethane prepolymer with low monomeric MDI content}}</ref>
4,4′-MDI is also used as an industrial strength adhesive, which is available to end consumers as various high-strength bottled glue preparations.<ref>{{US patent reference | number = 6884904 | y=2005 | m=04 | d=26 | inventor = Smith, A. K.; Goddard, R. J.; Paulsen, E. J. L. | title = MDI-based polyurethane prepolymer with low monomeric MDI content}}</ref>


==Safety==
==Safety==
MDI is the least hazardous of the commonly available isocyanates but is not benign.<ref>{{ cite book |editor1=Allport, D. C. |editor2=Gilbert, D. S. |editor3=Outterside, S. M. | year = 2003 | title = MDI and TDI: Safety, Health and the Environment: A Source Book and Practical Guide | publisher = Wiley | isbn = 978-0-471-95812-3 }}</ref> Its very low vapour pressure reduces its hazards during handling compared to the other major isocyanates ([[toluene diisocyanate|TDI]], [[hexamethylene diisocyanate|HDI]]). However, it, like the other isocyanates, is an allergen and sensitizer. Persons developing sensitivity to isocyanates may have dangerous systemic reactions to extremely small exposures, including respiratory failure. Handling MDI requires strict engineering controls and personal protective equipment.<ref>{{cite web | author = Almaguer, D.| title = Preventing Asthma and Death from MDI Exposure During Spray-on Truck Bed Liner and Related Applications | work = NIOSH Alert | id = DHHS (NIOSH) Publication No. 2006–149 | publisher = The National Institute for Occupational Safety and Health | date = September 2006 | url = https://www.cdc.gov/niosh/docs/2006-149/pdfs/2006-149.pdf | format = PDF | accessdate = 2012-08-14 |display-authors=etal}}</ref> Compared to other [[Cyanate|organic cyanates]], MDI has a relatively low human toxicity. It is a potentially violently reactive material towards water and other [[nucleophile]]s.
MDI, like the other isocyanates, is an allergen and sensitizer. Persons developing sensitivity to isocyanates may have dangerous systemic reactions to extremely small exposures, including respiratory failure. Handling MDI requires strict engineering controls and personal protective equipment.<ref>{{cite web | author = Almaguer, D.| title = Preventing Asthma and Death from MDI Exposure During Spray-on Truck Bed Liner and Related Applications | work = NIOSH Alert | id = DHHS (NIOSH) Publication No. 2006–149 | publisher = The National Institute for Occupational Safety and Health | date = September 2006 | url = https://www.cdc.gov/niosh/docs/2006-149/pdfs/2006-149.pdf | accessdate = 2012-08-14 |display-authors=etal}}</ref> It is a potentially violently reactive material towards water and other [[nucleophile]]s.


==References==
==References==
{{reflist}}
{{Reflist}}


==External links==
==External links==

Latest revision as of 06:55, 1 November 2023

4,4′-Methylene diphenyl diisocyanate
4,4'-methylene diphenyl diisocyanate
Names
Preferred IUPAC name
1,1′-Methylenebis(4-isocyanatobenzene)
Other names
  • Bis(4-isocyanatophenyl)methane
  • 1-Isocyanato-4-[(4-isocyanatophenyl)methyl]benzene
  • 4,4′-Methylene diphenyl diisocyanate
  • 4,4′-Diphenylmethane diisocyanate
  • Bayer Desmodur 44
  • Methylene bis(4-phenyl isocyanate)
  • Pure MDI
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
ECHA InfoCard 100.043.361 Edit this at Wikidata
EC Number
  • 4,4'-: 202-966-0
RTECS number
  • NQ9350000
UNII
  • InChI=1S/C15H10N2O2/c18-10-16-14-5-1-12(2-6-14)9-13-3-7-15(8-4-13)17-11-19/h1-8H,9H2 ☒N
    Key: UPMLOUAZCHDJJD-UHFFFAOYSA-N ☒N
  • O=C=NC(C=C2)=CC=C2CC1=CC=C(N=C=O)C=C1
  • O=C=N\c1ccc(cc1)Cc2ccc(\N=C=O)cc2
Properties
C15H10N2O2
Molar mass 250.25 g/mol
Appearance White or pale yellow solid
Density 1.230 g/cm3, solid
Melting point 40 °C (104 °F; 313 K)
Boiling point 314 °C (597 °F; 587 K)
Reacts
Vapor pressure 0.000005 mmHg (20 °C)[1]
Hazards
GHS labelling:
GHS07: Exclamation markGHS08: Health hazard
Danger
H315, H317, H319, H332, H334, H335, H351, H373
P201, P202, P260, P261, P264, P271, P272, P280, P281, P285, P302+P352, P304+P312, P304+P340, P304+P341, P305+P351+P338, P308+P313, P312, P314, P321, P332+P313, P333+P313, P337+P313, P342+P311, P362, P363, P403+P233, P405, P501
Flash point 212–214 °C (Cleveland open cup)
Lethal dose or concentration (LD, LC):
2200 mg/kg (mouse, oral)[2]
31,690 mg/kg (rat, oral)[2]
  • 369 mg/m3 (rat, 4 hr)
  • 380 mg/m3 (rat, 4 hr)
  • 178 mg/m3 (rat)[2]
NIOSH (US health exposure limits):
PEL (Permissible)
 C 0.2 mg/m3 (0.02 ppm)[1]
REL (Recommended)
 TWA 0.05 mg/m3 (0.005 ppm) C 0.2 mg/m3 (0.020 ppm) [10-minute][1]
IDLH (Immediate danger)
 75 mg/m3[1]
Related compounds
Related Isocyanates
Related compounds
 Polyurethane
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
☒N verify (what is checkY☒N ?)

Methylene diphenyl diisocyanate (MDI) is an aromatic diisocyanate. Three isomers are common, varying by the positions of the isocyanate groups around the rings: 2,2′-MDI, 2,4′-MDI, and 4,4′-MDI. The 4,4′ isomer is most widely used, and is also known as 4,4′-diphenylmethane diisocyanate.[3] This isomer is also known as Pure MDI. MDI reacts with polyols in the manufacture of polyurethane. It is the most produced diisocyanate, accounting for 61.3% of the global market in the year 2000.[4]

Production[edit]

Total world production of MDI and polymeric MDI is over 7.5 million tonnes per year (in 2017).

As of 2019, the largest producer was Wanhua Chemical Group.[5] Other major producers are Covestro,[6] BASF, Dow, Huntsman, Tosoh, Kumho Mitsui Chemicals. All major producers of MDI are members of the International Isocyanate Institute, whose aim is the promotion of the safe handling of MDI and TDI in the workplace, community and environment.

The first step of the production of MDI is the reaction of aniline and formaldehyde, using hydrochloric acid as a catalyst to produce 4,4'-Methylenedianiline and other diamine precursors, as well as their corresponding polyamines:

Then, these diamines are treated with phosgene to form a mixture of isocyanates, the isomer ratio being determined by the isomeric composition of the diamine. Two different reaction mechanisms for this transformation are possible, namely "phosgenations first" and "step-wise phosgenations".[7]

Distillation of the mixture gives a mixture of oligomeric polyisocyanates, known as polymeric MDI, and a mixture of MDI isomers which has a low 2,4′ isomer content. Further purification entails fractionation of the MDI isomer mixture.[8]

Reactivity of the isocyanate group[edit]

The positions of the isocyanate groups influences their reactivity. In 4,4′-MDI, the two isocyanate groups are equivalent but in 2,4′-MDI the two groups display highly differing reactivities. The group at the 4-position is approximately four times more reactive than the group at the 2-position due to steric hindrance.[4]

MDI isomers and polymer
MDI isomers and polymer

Applications[edit]

The major application of 4,4′-MDI is the production of rigid polyurethane.[9] These rigid polyurethane foams are good thermal insulators and used in nearly all freezers and refrigerators worldwide, as well as buildings. Typical polyols used are polyethylene adipate (a polyester) and poly(tetramethylene ether) glycol (a polyether).

4,4′-MDI is also used as an industrial strength adhesive, which is available to end consumers as various high-strength bottled glue preparations.[10]

Safety[edit]

MDI, like the other isocyanates, is an allergen and sensitizer. Persons developing sensitivity to isocyanates may have dangerous systemic reactions to extremely small exposures, including respiratory failure. Handling MDI requires strict engineering controls and personal protective equipment.[11] It is a potentially violently reactive material towards water and other nucleophiles.

References[edit]

  1. ^ a b c d NIOSH Pocket Guide to Chemical Hazards. "#0413". National Institute for Occupational Safety and Health (NIOSH).
  2. ^ a b c "Methylene bisphenyl isocyanate". Immediately Dangerous to Life or Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).
  3. ^ Pubchem. "4,4'-Diphenylmethane diisocyanate | C15H10N2O2 - PubChem". pubchem.ncbi.nlm.nih.gov. Retrieved 2017-06-25.
  4. ^ a b Randall, D.; Lee, S. (2003). The Polyurethanes Book. New York: Wiley. ISBN 978-0-470-85041-1.
  5. ^ Tullo, Alexander H. (29 July 2019). "C&EN's Global Top 50 chemical companies of 2018". Chemical & Engineering News. Vol. 97, no. 30. Retrieved 15 January 2020.
  6. ^ Gal, J. (2012-02-20). "To the Rescue". ICIS Chemical Business. Archived from the original on 2012-03-26. Retrieved 2020-01-15.
  7. ^ Boros, R. Zsanett; Koós, Tamás; Wafaa, Cheikh; Nehéz, Károly; Farkas, László; Viskolcz, Béla; Szőri, Milán (2018-08-16). "A theoretical study on the phosgenation of methylene diphenyl diamine (MDA)". Chemical Physics Letters. 706: 568–576. doi:10.1016/j.cplett.2018.06.024. ISSN 0009-2614. S2CID 102682388.
  8. ^ Six, C.; Richter, F. "Isocyanates, Organic". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a14_611. ISBN 978-3527306732.
  9. ^ Boustead, I. (2005). "Polyurethane rigid foam" (PDF). Eco-Profiles of the European Plastics Industry. Brussels: PlasticsEurope. Archived from the original (PDF) on 2013-09-25.
  10. ^ US patent 6884904, Smith, A. K.; Goddard, R. J.; Paulsen, E. J. L., "MDI-based polyurethane prepolymer with low monomeric MDI content", issued 2005-04-26 
  11. ^ Almaguer, D.; et al. (September 2006). "Preventing Asthma and Death from MDI Exposure During Spray-on Truck Bed Liner and Related Applications" (PDF). NIOSH Alert. The National Institute for Occupational Safety and Health. DHHS (NIOSH) Publication No. 2006–149. Retrieved 2012-08-14.

External links[edit]

Retrieved from "https://en.wikipedia.org/w/index.php?title=Methylene_diphenyl_diisocyanate&oldid=1182928127"