In 2019 the owner of an S Corp fail to pay his part of social security and medicare tax for the 3rd and 4th quarter, Can he deduct these unpaid taxes on his 2019 1120an S Corp?

no. I do not think so. he cannot claim the unpaid taxes on his 1040since they aren?t deductible on his income tax return. in general,as an owner/employee of S corp, you usually
receive a salary via aW2 unless the s corp suffers a loss. In generl, 2% shareholders MUST TAKE reasonable compensation from the S Corp as a W-2 employees.then, as an w2employee, you are responsible for fica tax.The employee's portion is paid through a payroll withholding of 6.2% and the employer, the S corp, will match the withheld amount. the s corp claims fica taxes on line 12 of Form 1120S.